Author Affiliations: Department of Gastroenterology (Yegin EG) and Department of Gastroenterology Surgery (Oymaci E), Bozyaka Training and Research Hospital, Izmir; Department of Radiology, Bulan?k State Hospital, Mus (Karatay E); Department of General Surgery, Ege University Faculty of Medicine, Izmir (Coker A), Turkey

Corresponding Author: Ender Gunes Yegin, MD, Department of Gastroenterology, Bozyaka Training and Research Hospital, Bahar Mh., Saim Cikrikci Cad. No: 59, Izmir 35170, Turkey (Tel: +90-232-250-5050; Email: drendergunes@hotmail.com)

 

© 2016, Hepatobiliary Pancreat Dis Int. All rights reserved.

doi: 10.1016/S1499-3872(16)60097-8

Published online May 17, 2016.

 

 

Contributors: YEG proposed the study. YEG, OE, KE and CA performed the research, wrote the first draft and analyzed the data. All authors contributed to the design and interpretation of the study and to further drafts. YEG is the guarantor.

Funding: None.

Ethical approval: Not needed.

Competing interest: No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this review article.

 

 

BACKGROUND: Hepatocellular carcinoma (HCC) is a complex and heterogeneous malignancy, frequently occurs in the setting of a chronically diseased organ, with multiple confounding factors making its management challenging. HCC represents one of the leading causes of cancer-related mortality globally with a rising trend of incidence in some of the developed countries, which indicates the need for better surgical and nonsurgical management strategies.

 

DATA SOURCES: PubMed database was searched for relevant articles in English on the issue of HCC management.

 

RESULTS: Surgical resection represents a potentially curative option for appropriate candidates with tumors detected at earlier stages and with well-preserved liver function. The long-term outcome of surgery is impaired by a high rate of recurrence. Surgical approaches are being challenged by local ablative therapies such as radiofrequency ablation and microwave ablation in selected patients. Liver transplantation offers potential cure for HCC and also correction of underlying liver disease, and minimizes the risk of recurrence, but is reserved for patients within a set of criteria proposed for a prudent allocation in the shortage of donor organs. Transcatheter locoregional therapies have become the palliative standard allowing local control for intermediate stage patients with noninvasive multinodular or large HCC who are beyond the potentially curative options. The significant survival benefit with the multikinase inhibitor sorafenib for advanced HCC has shifted the direction of research regarding systemic treatment toward molecular therapies targeting the disregulated pathways of hepatocarcinogenesis. Potential benefit is suggested from simultaneous or sequential multimodal therapies, and optimal combinations are being investigated. Despite the striking progress in preclinical studies of HCC immunotherapy and gene therapy, extensive clinical trials are required to achieve successful clinical applications of these innovative approaches.

 

CONCLUSION: Treatment decisions have become increasingly complex for HCC with the availability of multiple surgical and nonsurgical therapeutic options and require a comprehensive, multidisciplinary approach.

 

(Hepatobiliary Pancreat Dis Int 2016;15:234-256)

 

KEY WORDS: hepatocellular carcinoma; surgical liver resection; liver transplantation; locoregional therapies; molecular targeted systemic therapies; immunotherapy; gene therapy

Hepatocellular carcinoma (HCC) is one of the leading causes of cancer-related mortality worldwide and major global health problems. Approximately 782 000 new liver cancer cases were estimated to occur worldwide in 2012; it was reported as the fifth most common cancer in men and the ninth in women.^[1] Because of its high mortality rate (95%), it is the second most frequent cause of cancer-related death.^[1] The highest HCC incidence rates are seen in areas such as Southeast Asia, Middle and Western Africa. Although the incidence rates are much lower in most developed areas of the world, there has been a rise at alarming rates in the North America and in some parts of Europe.^[2] The age-adjusted incidence rates of HCC tripled between 1975 and 2005 in the United States (USA),^[3] while the prognosis of HCC remained poor with a 5-year survival rate of only 16.6% (liver and intrahepatic bile duct cancers).^[4] Patients are still infrequently diagnosed at earlier stages of HCC, which is in part related to the low utilization rates of surveillance in clinical practice.^[5] Treatment decisions have become increasingly complex for HCC with the availability of multiple therapeutic options, which require a comprehensive, multidisciplinary approach. This review provides comprehensive data on the current status of surgical or nonsurgical treatment of HCC.

 

 

The therapeutic approach to HCC is dictated by the stage of disease, patient’s performance status and comorbidities, available expertise, and lastly, the hepatic functional reserve and extent of portal hypertension (PHT), since many forms of therapies are related to the risk of worsening functional impairment of the liver. The therapeutic options include surgical therapies (liver resection [LR], liver transplantation [LT]), nonsurgical invasive therapies (e.g., radiofrequency ablation [RFA], percutaneous ethanol injection [PEI], transarterial chemoembolization [TACE]), and systemic medical therapies (e.g., sorafenib). Promising advanced radiotherapy (RT) technologies, immune-based and gene therapies are currently in development for HCC.

 

Although there is not one universal staging system for HCC, the Barcelona Clinic Liver Cancer (BCLC) system is a well-accepted algorithm for treatment allocation in the USA and Europe. It stratifies HCC disease into five stages (BCLC 0: very early; BCLC A: early; BCLC B: intermediate; BCLC C: advanced, and BCLC D: terminal stages) providing an integrated assessment of tumor extension (size, number, vascular invasion, and extrahepatic spread), liver function status by Child-Pugh system and patient’s performance status by ECOG (Eastern Cooperative Oncology Group), and links each prognostic stage with an evidence-based treatment strategy (Fig.). The BCLC staging system has gained wide acceptance because of its design conceptualizing various therapeutic options and providing prognostic prediction, and it has been endorsed by liver associations of the USA (American Association for the Study of Liver Diseases [AASLD])^[6] and Europe (European Association for the Study of the Liver-the European Organization for Research and Treatment of Cancer [EASL-EORTC]).^[7] The algorithm suggests no alternatives when patient is not a suitable candidate for the treatment offered in the defined stage; but a shift to the most suitable treatment in the next BCLC stage (stage migration concept) has been advised in those cases.^[7] There are some limitations of approaches like the BCLC system concerning the rigidity of the algorithm, absence of rapid evolving new therapeutic approaches and second-line or combined/sequential therapies, and the availability of options upon the resource and expertise, which may cause difficulties in adherence in the clinical practice.

 

Although the BCLC strategy recommends monotherapies, there is an increasing body of evidence suggesting the efficacy of simultaneous or sequential combination of the surgical and nonsurgical approaches which are increasingly used in clinical practice. Some of the widely investigated multimodal therapies include: nonoperative locoregional treatments for bridging patients to LT when the waiting time exceeds 6 months or for effective downstaging as a selection strategy who are initially outside the listing criteria, combination of ablative and transcatheter locoregional therapies especially for large HCC lesions, sorafenib as an adjuvant therapy after potentially curative resection or ablation to decrease recurrence, sorafenib with the intent of complementary inhibition of angiogenic factors induced due to the ischemic injury after TACE, combinations of molecular agents targeting different pathways or molecular targeted therapy-systemic chemotherapy combinations, and LR and salvage LT strategy to limit the use of grafts overall. Furthermore, combining standard HCC therapies with immune-based or gene therapies to decrease tumor recurrence or to enhance sensitivity to radiotherapy or systemic therapies generated some preclinical or clinical success and given their complementary mechanisms-of-action, these combinations will likely be improved in the future. Management of HCC has become an increasingly complex process with the availability of several surgical and nonsurgical therapeutic options and is best approached via a multidisciplinary team of hepatologists, interventional radiologists, liver transplant and hepatobiliary surgeons, pathologists, medical oncologists for an optimum individualized management for each patient.

 

 

Surgical resection is a potentially curative option for a solitary anatomically resectable HCC confined to the liver without major vascular invasion in medically fit patients with adequate liver functional reserve. LR is the treatment of choice in noncirrhotic patients within these criteria, and also should be considered in selected cirrhotic patients with well-preserved liver function (generally Child-Pugh class A without PHT). Although patients with solitary HCC with a diameter of less than 5 cm are generally regarded as the ideal candidates for LR, there is some controversy over LR for larger HCCs and resectable multifocal disease concerning the unsatisfactory long-term results. In BCLC classification, BCLC stage 0 (very early stage) is defined by a single HCC ≤2 cm with Child-Pugh class A liver function and ECOG score 0, and BCLC stage A (early stage) is defined by single nodule or up to three nodules ≤3 cm with Child-Pugh class A-B liver function and ECOG score 0. Based on the BCLC treatment algorithm, patients at BCLC stage 0 and at BCLC stage A with a solitary nodule can be treated with LR if portal pressure and billirubin are normal (Fig.)

 

Microscopic vascular invasion (MVI) is an important risk factor of recurrence and worse survival after LR.^[8,9] It is different from macrovascular invasion, requires histological examination, and often difficult to detect by preoperatively using imaging modalities. Larger size, multinodularity, alpha-fetoprotein (AFP) level >400 ng/L, high levels of preoperative descarboxyprothrombin (DCP), lectin-bound AFP (L3-AFP) positivity, and histologic grade have been shown to predict MVI preoperatively.^[10-15] The incidence of MVI is shown to increase proportionally to the size of the tumor (≤3 cm, 25%; 3.1-5 cm, 40%; 5.1-6.5 cm, 55%; >6.5 cm, 63%) (P<0.005).^[16] Multinodular HCC is also more significantly associated with a worse prognosis than solitary tumors; one study suggested LR for multinodular HCC if tumor could be removed by one-block resection with an adequate liver function reserve.^[17] Gene expression profiles in tumor and adjacent tissues may add further important prognostic information beyond these standard histological predictors. In one study, the G3 (tumor-related) signature and poor-survival (nontumor, cirrhotic tissue-related) signature along with satellites were revealed as the independent predictors of tumor recurrence among several other variables like tumor size, vascular invasion, degree of differentiation and BCLC stage.^[18]

 

Perioperative mortality is now expected to be less than 5%^[19] because of advances in preoperative planning, postoperative care, surgical concept and techniques translating to and being effectively applied in LR for HCC. Conventional extensive resection approach has been transforming to the minimally invasive precise LR concept, with the optimization of modern technologies and sophisticated surgical techniques, including advanced medical imaging systems like three-dimensional (3-D) reconstruction images and intraoperative ultrasound navigation^[20] leading to safer resection margins sparing the vascular and biliary structures, optimal parenchymal transection strategies associated with lower rates of blood loss, and techniques like methylene blue staining for guiding the anatomic resection^{[21, 22]} with the aim of complete resection of the lesion while preserving sufficient liver volume and integrity of the vascular and biliary structures and limiting the complications.^[23] Laparoscopic LR (LLR) for HCC represents a less invasive and safer alternative to open LR (OLR), especially for cirrhotic patients. LLR has been increasingly applied over the past 5 years with the accompanying advances in the technique in the era of minimal invasive surgery. In Japan, LLR comprises up to 40% of all LR cases including those treated in community hospitals, while in North America and Europe, LLR is performed mostly in referral centers by surgeons with adequate expertise.^[24] Although LLR and OLR for HCC have not been compared in a randomized controlled trial (RCT), 5 meta-analyses investigating the short- and long-term results of LLR for HCC suggested perioperative benefits like reduced blood loss and transfusion requirements, lower rates of postoperative morbidity (specially ascites, liver failure, pulmonary complications), and shorter hospitalization when compared to OLR; also, long-term oncologic outcomes like surgical margin status, survival and recurrence were similar to those of OLR.^[25-29] The benefit of minimizing intra-abdominal adhesions^[30] favors the laparoscopic approach for HCC in which the possibility of repetitive surgery for recurrence or LT could be expected. With the growing evidence in favor of LLR and increasingly adoption of the technical skill by hepatobiliary surgeons, LLR could have more impact on the therapeutic strategy of HCC in the near future. Despite the benefits, LLR has some inherent limitations like amplification of tremor, 2-D vision of the operative field, restricted instrument motion, and the long learning curve. Robotic-assisted technology was introduced in part to overcome some of these limitations. Da Vinci surgical robotic system (Intuitive Surgical, Sunnyvale, CA, USA) offers intuitive translation of master control movements to the tip, permits more freedom in movements by the articulated tips rivaling the human hand, a 3-D view of the surgical field with improved depth perception, filtration of physiologic tremor, and remote control by the surgeon from a console, potentially providing better maneuverability, ergonomics, improved precision, and longer operation tolerance. However, total medical costs were significantly higher for LR with robotic technology^[31] than with LLR. Also, the learning curve of the robotic surgery compared with conventional laparoscopy remains poorly analyzed. From the oncological view, a worrying disadvantage is the lack of tactile sensation with this technology, and to ensure safe resection margins, a liberal use of intraoperative laparoscopic ultrasonography has been advocated^[32,33] for robotic-assisted LR (RALR). A recent systematical review of 29 studies comparing the surgical results of LR and RALR in all kinds of liver neoplasms included 9 of the studies for the meta-analysis.^[34] The meta-analysis results suggested that perioperative outcomes of RALR regarding blood loss, transfusion rate, postoperative morbidity and length of hospital stay were comparable to those of LLR, while a longer operative time was noted for RALR. Long-term oncological outcomes remained unclear due to the lack of adequate representative data.^[34] RALR for HCC is still in its developing stage; a decisive conclusion can only be drawn after the obtainment of high-quality evidence from larger randomized studies separately designed for HCC, stating the long-term oncological outcomes as well as cost-benefit analysis.

 

Preoperative assessment of the function and volume of the remnant liver is mandatory for major LR or underlying liver disease to minimize the risk of postoperative liver failure and death. The Child-Pugh classification and Model for End-stage Liver Disease (MELD) score are crude estimates for stratifying the surgical risk of patients with cirrhosis. The presence of PHT implies a poorer survival. Splenomegaly, abdominal collaterals, esophagogastric varices, and a platelet count <100 000/mm³ indicate the presence of PHT. In the absence of these, wedged hepatic venous pressure gradient can be assessed by hepatic vein catheterization. Resection of 2 or more segments is not recommended in patients with PHT.^[35] Preoperative volumetric measurement by 3-D computerized tomography determines the future liver remnant (FLR) volume and selects the patients who will be benefited from preoperative portal vein embolization (PVE) to increase the volume of the liver remnant.^[36] The volume limit for safe resection ranges from 20% to 30% FLR of total liver volume (TLV) in patients with a normal liver^[37] and >40% FLR of TLV in patients with well-compensated cirrhosis.^[36] Additionally, many centers in Asia use hepatic clearance of indocyanine green from systemic circulation at 15 minutes (ICG-15) which reflects uptake function of the liver and the hepatic blood flow to define the extent of liver volume that can be safely resected and to avoid PHT related complications. It is recommended by the recent Japanese evidence-based clinical guidelines for HCC,^[38] while it is not widely used in the Western countries. Makuuchi et al^[39] have incorporated the ICG-15, serum bilirubin level and the presence of ascites into a decision algorithm. In general, the optimal candidates are considered who have an ICG-15 ≤20% for LR in patients with normal bilirubin levels and no ascites. Low postoperative mortality rates have been reported using this algorithm in a tertiary referral center where 1056 hepatic resections were performed.^[40] Preoperative PVE (alone or after a previous TACE) is increasingly employed with the intention to induce atrophy in the embolized liver portion and compensatory hypertrophy in the unaffected liver portion to prevent postoperative liver failure in patients with a low estimated FLR to TLV ratio. A meta-analysis of 37 studies involving 1088 patients showed that PVE is a safe and effective (morbidity rate of 2.2% without mortality) procedure to prevent post-resection liver failure.^[41]

 

Despite potentially curative resection, the 5-year recurrence rate of HCC can be as high as 80%.^[12] The benefit of anatomical resection or a wider resection margin (2 cm compared to a 1-cm margin) is suggested.^[42] In a large series approximately two thirds of recurrences occurred early (<2 years) after resection, and parameters related to tumor invasiveness (presence of MVI, high serum AFP level) and surgical procedure (nonanatomical resection) were found as contributing factors suggesting dissemination of the original tumor, while variables such as tumor multiplicity and the grade of hepatitis activity related to the increased carcinogenicity of the cirrhotic background were related to late recurrence^[12] which may correspond to ‘de novo’ tumors. Given the high rates of recurrence following resection, TACE^{[43, 44]} for neoadjuvant therapy and several adjuvant therapies such as systemic and intraarterial chemotherapy,^[45] intraarterial infusion of iodine-131-lipiodol (¹³¹I-lipiodol),^[46] sorafenib,^[47] TACE,^[48] acyclic retinoids,^[49] and the immune-based therapies have been investigated. The recent progress in the immunotherapy field is discussed below. The recently resulted randomized phase III study comparing sorafenib with placebo as adjuvant therapy revealed similar median recurrence-free survival (RFS) between the two groups (33.3 vs 33.7 months, P=0.26) and concluded that sorafenib is not an effective intervention in the adjuvant setting after potentially curative therapies (resection or ablation).^[47]

 

Traditional oncologic endpoints such as time to progression (TTP) or overall survival (OS) may be insufficient as the only measures to assess the clinical benefit of therapeutic interventions, especially for tumors including HCC with a poor OS. Health-related quality of life (HRQoL) has become an important endpoint in clinical trials as a multi-dimensional concept addressing multi-item life and symptom domains like physical, mental and emotional functioning, social/family well-being and global health. HRQoL questionnaires like European Organization for Research and Treatment of Cancer Quality of Life Questionnaire-Core 30 (EORTC QLQ-C30) and the Functional Assessment of Cancer Therapy-Hepatobiliary Questionnaire (FACT-Hep), and Functional Assessment of Cancer Therapy Hepatobiliary Symptom Index (FHSI-8) have been increasingly used to assess the effect of LR, TACE or RFA in HCC studies, although to date, existing HRQoL measures have not been extensively implemented in clinical care. A non-randomized multicenter study^[50] comparing the QoL changes using questionnaires (EORTC QLQ-C30 and QLQ-HCC18) in 171 HCC patients who underwent surgery, ablation or embolization treatments reported worse outcomes in many QoL domains with ablation than embolization or surgery; embolization revealed similar QoL outcomes as surgery in this study. Similarly, in one study, LR provided better QoL by FACT-Hep questionnaire at 24 months compared with RFA, and also compared with TACE.^[51] The QoL data from more researches are needed to provide evidence for a patient-centered treatment approach by indicating high-risk groups who should be prioritized for therapeutic interventions expected to improve the survivors’ HRQoL and who are in greater need for psychosocial support.

 

 

Liver transplantation is a potentially curative therapeutic modality for carefully selected candidates; it minimizes the risk of tumor recurrence by removing both intrahepatic tumor foci and carcinogenic cirrhotic background and provides the best long-term outcome for patients with moderate to severe cirrhosis by correcting the functional liver impairment. According to the BCLC decision algorithm, LT is offered as an initial treatment for patients with BCLC stage A (early stage) for whom multiple tumor foci, liver function status or presence of PHT does not permit surgical LR with curative intent (Fig.).

 

The landmark study by Mazzaferro et al^[52] published in 1996 stated the Milan criteria (single tumor ≤5 cm or up to three nodules ≤3 cm in diameter, without macroscopic vascular invasion, regional nodal or extrahepatic metastases) to define the most appropriate transplant candidates with 4-year OS and relapse-free survival rates of 85% and 92%, respectively. A meta-analysis reviewing 90 studies including 17 780 patients over 15 years confirmed the significant survival benefit for patients meeting the Milan criteria versus those beyond the Milan criteria with the hazard ratio of 1.68 [95% confidence interval (CI): 1.39-2.03].^[53] The Milan criteria have been accepted as an international standard for prioritization and delisting policies worldwide and have been adopted by the United Network for Organ Sharing (UNOS) in the USA to limit the LT to HCC patients who are expected to have the highest benefit for a prudent allocation in the shortage of available donor organs. HCC patients with UNOS T2 tumors (one nodule 2-5 cm or three or fewer nodules each ≤3 cm) are assigned 22 MELD points, a higher exception score^[54] in order to equalize the mortality risk predicted by MELD score.

 

Over the past years, various sets of expanded criteria were introduced; however, there has been an ongoing debate over the optimized expansion beyond the Milan criteria. According to the analysis by Volk et al,^[55] a 5-year post-transplant survival rate exceeding 61% would justify expansion of the Milan criteria to allow the benefit from LT to be outweighed by the harm to other patients on the waiting list. An expanded set of criteria for patients with a solitary HCC tumor ≤6.5 cm, or up to three lesions each <4.5 cm (total tumor diameter ≤8 cm) has been proposed by Yao et al^[56] at the University of California San Francisco (UCSF) with a survival of 90% and 75.2% at 1 and 5 years, respectively, after LT. In patients with HCC exceeding these criteria, the 1-year survival rate decreased to 50% (P=0.0005). Many studies have shown similar results suggesting that liberalizing LT for patients with more nodules or larger tumors and without MVI can achieve outcomes comparable to those of more restrictive Milan criteria. The up-to-seven criteria, Asan criteria and Hangzhou criteria are some of the other selection criteria proposed to expand the Milan criteria with acceptable post-transplant 5-year survival rates of 71.2%,^[57] 72.0%,^[58] and 72.3%,^[59] respectively. Nevertheless, the 2010 International Consensus Conference on LT for HCC has not endorsed any of the expanded criteria beyond the Milan criteria for deceased donation considering the negative impact of the expansion on mortality of others on the waiting list in the persisting shortage of donors.^[54] Practices may differ outside the USA. The Transplantation Society of Australia and New Zealand expanded the eligibility criteria and moved to use the UCSF criteria.

 

Other parameters have been suggested to predict poor post-transplant results besides tumor size and number. Prediction of tumor recurrence was improved significantly by a model that incorporates AFP to the Milan criteria in one study;^[60] AFP level and total tumor volume rather than the Milan or UCSF criteria depending on tumor size and number could predict post-transplant outcome in another study.^[61] The Hangzhou criteria also include AFP level, and found to have prognostic predicting capacity when stratified according to the tumor burden and AFP level.^[62] Presence of MVI detected at pathology is a well-known risk factor related with recurrence after LR or LT,^{[9, 13, 57]} but its recognition cannot be reliably made by radiological modalities prior to LT, which limits its usefulness for pretransplant decision making criteria. Potential surrogates have been investigated, and besides tumor size, multinodularity and histological grade, the preoperative high levels of DCP were found to be correlated with the presence of MVI.^[63,64] Some predictive models were designed for estimation of the long-term survival benefit or for prediction of recurrence after LT such as the Metroticket,^{[57, 65]} AFP^[60] and Markov^[66] prediction models.

 

The concept of salvage LT, performing LT in case of recurrence after an intended curative resection and reallocating the livers not used for the patients initially being resected is an alternative strategy that could lead to an overall survival benefit. A study using a Markov simulation model based on the data from the literature revealed salvage LT as an optimal strategy to adopt where the 5-year survival rate after LT is under 60%, and suggested a gain in life expectancy to the remaining waiting list patients in countries where a larger proportion of HCC patients spend a long time on the waiting list.^[67] Another study^[68] reported a higher operative mortality, an increased risk of recurrence, and a low transplant ability, which lower the 5-year OS (41% vs 61%, P=0.03) for salvage LT compared to primary LT. It was proposed that management after primary resection could be guided by histological parameters from the resected specimen, and that patients who have a high-risk profile for recurrence (MVI, satellite nodules, tumor size >3 cm, poorly differentiated tumor) could be scheduled for LT after primary resection, whereas those who have a low-risk profile could be followed up and subjected to salvage LT upon detection of recurrence.^{[69, 70]}

 

Several neoadjuvant approaches have been proposed for HCC patients within the transplant criteria as a bridge to LT in order to decrease the drop-out rate until the availability of a donor organ. The role of TACE,^[71,72] TACE with drug-eluting beads (DEB-TACE),^[73] transarterial radioembolization (TARE) with yttrium-90 (⁹⁰Y) microspheres,^[74] RFA,^{[75, 76]} conformal RT,^[77] and sorafenib^[78] as bridging therapies has been investigated. The practice of using bridging therapies is common in many transplant centers although evidence from prospective randomized studies on the impact of treatment on the waiting list is lacking. The 2010 International Consensus Conference on LT for HCC concluded that bridging treatments might be considered for patients with UNOS T2 HCC whose waiting time on the list would likely exceed 6 months.^[54] An approach being used by some institutions is down-staging treatments for more advanced HCC to achieve the accepted criteria for eligibility for LT. Even though there are some studies demonstrating an improved post-transplant disease-free survival with successful PEI, RFA, TACE, TARE with ⁹⁰Y microspheres down-staging treatments,^[79-81] it is a weakly recommended tool for determining eligibility in guidelines, unless in the context of prospective studies.^{[7, 82]} The possible mechanism of the trend toward better post-transplant outcomes with bridging and down-staging treatments may be the selection of tumors with a more favorable biology related to vascular invasion and differentiation grade determined by achievement of a major local tumor response.

 

Despite the stringent selection criteria for LT, recurrent HCC occurs in approximately 20% of patients,^[83] usually seen within the first 2 years limiting the median survival to about 1 year.^[84] It has been suggested that immunosuppressive strategy should be modified from calcineurin inhibitor (CNI)-based regimen to mammalian target of rapamycin inhibitors (mTORis)-based regimen to reduce the risk of post-transplant tumor recurrence. mTORis are known to have antiangiogenic, antiproliferative, and antitumor effects^[85] other than the immunosuppressive activity. A meta-analysis^[86] demonstrated that sirolimus (SRL)-based regimens were associated with lower HCC recurrence (OR=0.30; 95% CI: 0.16-0.55; P<0.001), and overall mortality (OR=0.35; 95% CI: 0.20-0.61; P<0.001) compared with CNI-based regimens, confirming the efficacy reported in a previous meta-analysis which also had shown the safety with regard to acute rejection and hepatic artery thrombosis.^[87] A more recent systematic review^[88] compared both SRL and everolimus (EVL) with CNI use and found that EVL was significantly associated with a lower recurrence rate of HCC, compared with SRL or CNIs (4.1% vs 10.5% vs 13.8%, respectively, P<0.05), although a straightforward comparison may not be appropriate because of the differences in the follow-up period and risk factors for recurrence. Despite encouraging findings favor the use of mTORi-based immunosuppression, prospective data from a phase III randomized trial are awaited to prove the post-transplant oncological benefit of mTORis.^[89]

 

There is no consensus regarding the optimal treatment strategy for post-transplant HCC recurrence due to few well-conducted studies addressing this issue. Theoretically, the wide range treatment options for HCC can also be employed for its recurrence. A recent systemic review^[84] reported the best outcomes for surgical resection with 42 months of survival generally with an uneventful postoperative period, although favorable tumor localization and size and good patient performance status allowing resection may have impacted the survival benefit obtained. The efficacy of RFA in treating small HCCs may be extrapolated to post-transplant recurrence, although comparison with LR is not available for this setting. TACE is a frequently applied post-transplant locoregional treatment and generally is well-tolerated and safe.^[84] TACE resulted in a median survival of 11.2 months in a post-transplant setting.^[84] When the presentation is spread not allowing the locoregional approaches, systemic treatments are warranted. The results from some studies suggest survival benefit with the administration of sorafenib despite some notable toxicities requiring dose reduction or discontinuation.^[90-93] Concomitant use of sorafenib and mTORi has gained interest, since a synergistic effect on improving survival has been advocated for this combination.^{[94, 95]} The toxicity and efficacy should be further investigated before considering the sorafenib or its combination with mTORi as valid options.

 

 

Many nonsurgical locoregional options are available for patients who are not candidates for LR or LT and are categorized as ablative and transcatheter locoregional therapies.

 

Ablative therapies should be considered for early HCC stages (BCLC stage 0 and A) (Fig.), and can serve as both palliative and potentially curative interventions. Ablative techniques include ethanol or acetic acid injection, RFA, cryoablation, microwave ablation (MWA), laser thermal ablation, irreversible electroporation, and high-intensity focused ultrasound.

 

The conventional PEI technique is a relatively well-tolerated, inexpensive and safe procedure that requires minimal technological equipment. It induces tumor necrosis as a result of dehydration and protein denaturation in tumor cells, followed by vascular thrombosis of small vessels and ischemia of the tumor. In the RFA technique, the alternating current of radiofrequency waves passing down from the electrode tip into the tumoral tissue induces ionic agitation and gradual frictional heating, resulting in tissue destruction by desiccation and coagulative necrosis. Four meta-analyses from randomized trials, confirmed RFA’s superiority to PEI concerning the survival rate and risk of local recurrence, particularly for tumors >2 cm, indicating RFA as the standard ablative treatment.^[96-99] For tumors >20 mm in diameter, the probability of achieving a complete necrosis is greater than that with RFA than PEI, reported as 68.1% vs 26.3% in a RCT.^[100] RFA has the capacity of ablating the peripheral region beyond the tumor borders and it is recommended to produce a 5-10 mm thick safety margin in order to eradicate the microscopic invasions. RFA of lesions in a subcapsular location or adjacent to critical structures, like kidney, colon, gallbladder, or hepatic hilum increases the risk of thermal injury to adjacent tissues and major complications. PEI still play a role where RFA is not feasible because of the high-risk location of the tumor which was reported to be around 9%.^[101] Also, PEI procedure may be more suitable for lesions adjacent to large blood vessels where a complete tumor eradication may not be achieved by RFA due to the perfusion-mediated cooling effect by vessels (heat-sink effect).

 

It has been suggested that RFA can be an alternative treatment that can compete with LR for patients with early-stage HCC, with a 5-year survival rate of approximately 70% reported in many series.^[102-104] A meta-analysis including 13 studies with a total of 2535 patients and tumor size ranging from 1.8 to 3.8 cm found that the 5-year OS rate was significantly higher (OR=0.60; 95% CI: 0.43-0.84) and the 5-year recurrence rate was significantly lower (OR=1.68; 95% CI: 1.21-2.34) in patients treated with LR than RFA.^[105] The decision between the two treatments should depend on the determinants of outcome, perioperative mortality risk and expertise of the institution. The equally effective outcomes with RFA treatment have been reported for very small HCC (<2 cm) tumors located in favorable locations for ablation in patients with Child-Pugh A liver function.^{[103, 104]} It seems reasonable to consider RFA as the first-line option in these patients. The probability of achieving complete necrosis with a safety margin is known to be size dependent with RFA. In a histological study of the explanted livers of patients who underwent RFA as a bridge treatment to LT, 87% of tumors ≤2.5 cm and 53% of tumors >2.5 cm were found to be successfully treated with RFA.^[106] A retrospective study found that the efficacy of RFA including OS and RFS rates was better than LR for HCC smaller than 2 cm, especially for those with central location.^[104]

 

Available evidence suggests that combined ablative and transcatheter locoregional therapies may be more effective, especially for large HCC lesions. A meta-analysis of eight randomized controlled trials including 598 patients concluded that RFA and TACE combination was associated with a significantly higher OS rate in patients with intermediate-size (3 cm<tumor size≤5 cm) and large-size HCC (>5 cm) than RFA monotherapy, but not in patients with small HCC (≤3 cm).^[107] No significant differences were found in major complications between the two treatments (P=0.79).^[107] Some synergistic effect is suggested for the combination of these two interventional treatments. TACE, by reducing the perfusion-mediated cooling effect (heat-sink effect) of hepatic blood flow with the occlusion hepatic arterial flow, enhances the heat delivery of RFA treatment and increases the thermal ablation zone.^[108]

 

MWA is an emerging thermal ablative technique alternative to RFA that may allow larger ablation zones and may be less affected by vessels located proximal of the tumor. Equivalent therapeutic effects, complication rates, and rates of residual tumor foci were reported in a RCT.^[109] Further studies are necessary to compare MWA with RFA and LR.

 

Transcatheter locoregional therapies have become the palliative standard of care for intermediate stage (BCLC B) patients with multinodular or large HCC in the absence of macrovascular invasion and extrahepatic spread with Child-Pugh A-B liver function and preserved performance status, who are beyond potentially curative options (Fig.). Accurate prognostic stratification of more advanced BCLC stages may affect the therapeutic decisions; in a recent study, BCLC stage C HCC patients with Cancer of the Liver Italian Program (CLIP) score 0-2 captured benefit by TACE treatment (OS of 13 months for CLIP scores 0-2 vs 4 months for best supportive care, P=0.001),^[110] indicating the disease heterogeneity and a need for a better prognostic stratification for advanced BCLC stages. Transcatheter tumor therapies involve selective catheter-based hepatic arterial infusion of chemotherapeutic agents, embolic particles, or radioactive materials targeting the feeding vessel of the tumors under imaging guidance and include transcatheter arterial chemo-infusion, transarterial bland embolization (TAE), TACE, DEB-TACE, and TARE. TACE is the most commonly used technique and involves transcatheter administration of intraarterial chemotherapy often suspended in lipiodol followed by embolization with the goal to prevent washout of the drug and to induce ischemic necrosis. A standardized protocol concerning procedural technique, choice of chemotherapeutic agent (cisplatin, mitomycin-C and doxorubicin alone or in combination) or embolizing agent (polyvinyl alcohol particles, starch microspheres, metallic coils, gelatin sponge particles [Gelfoam]), or optimal retreatment schedule has not been established yet.

 

A meta-analysis of 14 studies showed a survival benefit with TACE compared to the controls; sensitivity analysis revealed a significant benefit of TACE with cisplatin or doxorubicin from four studies but no benefit with TAE alone from three studies.^[111] Two other meta-analyses reported a significant survival benefit with TACE, but did not reveal a difference in survival with TACE over TAE.^{[112, 113]} Despite some controversial results, TACE rather than bland embolization alone is recommended in the AASLD and the EASL-EORTC guidelines.^{[6, 7]}

 

DEB-TACE was introduced as chemotherapy embedded embolic microspheres allowing occlusion of the feeding arteries as well the delivery of chemotherapeutic agent in a sustained and controlled manner within the tumor nodule. It has gained acceptance owing to the improved safety and tolerability profile and replaced conventional TACE at many centers. No difference in tumor response or disease control between two treatments were found in two meta-analyses,^{[114, 115]} whereas a recent meta-analysis reported a significantly better tumor response (OR=1.92; 95% CI: 1.34-2.77; P=0.0004) with significantly higher one-year and 2-year survival rates for DEB-TACE than for conventional TACE.^[116] The pharmacokinetic data demonstrated the lower peak and cumulative levels of doxorubicin in the systemic circulation with the use of drug-eluting beads loaded with doxorubicin compared to conventional TACE,^{[117, 118]} significantly reducing hepatic and systemic toxic effects including liver toxicity and grade 3 and 4 adverse events.^{[118, 119]}

 

A post-embolization syndrome involving right upper quadrant pain, nausea, intestinal ileus, fatigue, and fever has been reported as the most common adverse effect of TACE procedure, which is usually self-limited. Other complications include liver failure, bile duct injury, gastroduodenal ulceration, and pulmonary or cerebral lipiodol embolization. Performing TACE treatment may lead to severe complications and death in the case of extensive involvement necessitating non-selective embolization, impaired portal blood flow and poor hepatic functional reserve due to increased risk of ischemic necrosis and liver failure. Cannulation of the feeding artery as selective as possible is recommended to minimize the risk. Macroscopic vascular invasion, extrahepatic spread, main portal vein thrombosis (PVT), severe decompensated liver disease, and massive multinodular tumor involvement of entire lobes are considered major contraindications for TACE.^[120]

 

One factor that may potentially interfere with the effectiveness of TACE is the upregulation of TACE-induced angiogenic factors like vascular endothelial growth factor (VEGF) due to ischemia, which is associated with poor prognosis.^[121] Therefore, TACE in combination with agents with antiangiogenic properties like sorafenib has been studied in randomized trials. The results from two randomized trials^{[122, 123]} suggested that combined sorafenib and TACE might play a role in prolongation of TTP and better disease control in intermediate stage HCC patients compared with chemoembolization treatments.

 

TARE is an alternative catheter-based approach delivering a potent dose of radiation therapy preferentially to tumor foci and relatively sparing the normal liver parenchyma. Different radiopharmaceuticals like ¹³¹I-lipiodol, Rhenium-188 lipiodol, and ⁹⁰Y microspheres have been utilized; the most commonly used is ⁹⁰Y which is a β-emitting isotope. Several studies published in the last 5 years have reported promising clinical efficacy in terms of survival and safety with the use of TARE comparable to TACE for the intermediate stages. In a retrospective comparative analysis of 122 patients treated with TACE and 123 patients treated with TARE with ⁹⁰Y, response rates tend to be higher in the TARE group (49% vs 36%, P=0.104) and TTP was significantly longer following TARE (13.3 vs 8.4 months, P=0.046), although the median survival was not significantly different between the TARE and TACE groups (20.5 vs 17.4 months, P=0.232).^[124] TARE was better tolerated, with significantly less toxicity than chemoembolization.^[124] The minimal embolic effects of ⁹⁰Y allow TARE to be used in selected populations who are not good candidates for TACE like patients with extensive bilobar involvement or at advanced stages due to PVT. Studies^[125-127] have reported a median survival of 5.6-10 months in TARE with ⁹⁰Y treated patients with PVT, parallel to the survival results of median 6.5-10.7 months obtained with sorafenib treatment for advanced HCC.^{[128, 129]} TARE appears to have a favorable toxicity profile. Despite encouraging data, this treatment needs to be investigated in RCTs in head-to-head comparisons with chemoembolization techniques or sorafenib in patients at intermediate or advanced stage.

 

 

Many HCC patients presenting with advanced stage or showing progression upon locoregional therapies are referred for systemic therapies. Patients with mild tumor-related symptoms, macrovascular invasion and/or extrahepatic spread with Child-Pugh A-B liver function are considered to have BCLC stage C (advanced stage) disease, and systemic therapy is the primary treatment option for patients at this stage (Fig.).

 

Clinical studies investigating conventional cytotoxic chemotherapy regimens have reported low response rates without any OS benefit and increased treatment related toxicity. Doxorubicin has long been considered as the reference drug, but intravenous single agent doxorubicin provided limited benefit with a median survival of 3.7-7.2 months^[130-132] without demonstrating any survival benefit but severe complications such as septicemia and cardiotoxicity. Combined with other agents (cisplatin, interferon [IFN] alpha-2b, doxorubicin, fluorouracil [FU] [PIAF] regimen) as a single agent, it induced a more favorable response rate of 20.9% in contrast to 10.5%, but there was no difference in survival in a phase III trial.^[130]A prospective, randomized, multicenter phase IIB trial of combined doxorubicin and sorafenib against standard-of-care sorafenib in advanced HCC is ongoing.^[133] Other systemic chemotherapeutic agents such as gemcitabine, 5-FU, cisplatin, capecitabine or combined regimens were related to only marginal improvements in survival or associated with unacceptable toxicities. Consequently, in the absence of a convincing survival advantage with any single agent or combination regimen, guidelines do not support the use of any cytotoxic chemotherapy as standard of care for HCC.^{[6, 7, 134]} Systemic cytotoxic chemotherapy may be discussed for patients with adequate liver function and performance status who demonstrate progression or cannot tolerate sorafenib or when no other options are locally available, preferably within the context of a clinical trial. Multiple other treatment modalities such as hormone agents like tamoxifen, megestrol, octreotide, and lanreotide have also been investigated but have not demonstrated clinically relevant antitumoral effect or survival benefit, and are not currently recommended.

 

Hepatocarcinogenesis is a complex multistep event and detailed molecular pathogenesis is not completely clarified. The process is initiated by environmental factors that lead to chronic inflammation, and the accumulation of multiple genetic and epigenetic changes alter the expression of oncogenes and tumor suppressor genes and drive the progression of normal hepatocytes to dysplasia and neoplasia. The key signaling pathways of hepatocarcinogenesis include epidermal growth factor receptor (EGFR), VEGF receptor (VEGFR), fibroblast growth factor receptor (FGFR), platelet-derived growth factor receptor (PDGFR), insulin-like growth factor receptor (IGFR), Ras/PI3K/PTEN/Akt/mTOR, Ras/RAF/MEK/ERK signaling pathways. Aberrant activation of these pathways is associated with resistance to apoptosis, unrestricted cellular proliferation, differentiation, angiogenesis, invasiveness and metastasis. Sorafenib is a multitargeted tyrosine kinase inhibitor (TKI) acting on Raf serine/threonine kinases, VEGFR (VEGFR-1, VEGFR-2, VEGFR-3), and PDGFR-β.^[135] Sorafenib emerged as a first systemic treatment that resulted in a survival benefit compared with placebo in two RCTs, thereby has become the standard systemic treatment for advanced HCC. In the phase III RCT, the SHARP trial, that involved 602 advanced HCC patients mainly from America and Europe, reported a significant survival benefit represented by a 31% relative reduction in the risk of death with a median OS rate in the sorafenib group of 10.7 months compared to 7.9 months in the placebo group (HR=0.69; 95% CI: 0.55-0.87; P<0.001).^[128] Similarly, a significant survival advantage was demonstrated in the second phase III RCT, which was conducted in 226 patients from Asian-Pacific population with a median OS of 6.5 months in the sorafenib group versus 4.2 months in the placebo group (HR=0.68; 95% CI: 0.50-0.93; P=0.014).^[129] The benefit of OS was less in the Asian-Pacific trial than in the SHARP trial; this may be related to the differences in ethnic populations and the etiology of the underlying cirrhosis leading to distinct outcomes, and emphasizes the heterogenous and complex nature of HCC and the difficulty to achieve similar and reproducible results. Extrahepatic spread (with: P=0.13 vs without: P<0.0001), normal AFP level (P=0.15 vs elevated: P=0.0006), and elevated serum bilirubin level (P=0.06 vs normal: P=0.0009) were identified as the parameters affecting the benefit of sorafenib therapy in advanced HCC patients in a latter systematic review of six trials including three RCTs.^[136] Treatment was well-tolerated in both SHARP and Asian-Pacific RCTs of sorafenib, consisting of mostly patients with preserved liver function; the majority of drug related toxicities were grade 1 or 2 in nature with the most common adverse events including diarrhea, fatigue, weight loss and hand-foot skin reaction. In the final analysis of a post-marketing study including a large, global database of >3000 patients assessing the tolerability and outcome of sorafenib in real-life practice, the drug-related adverse effect profile of sorafenib appeared to be similar for Child-Pugh B and Child-Pugh A patients, although serious adverse effects were more commonly experienced by Child-Pugh B patients.^[137] Given the poor prognosis and high risk of drug-related toxicity for patients in Child-Pugh C class, most physicians would not use sorafenib to these patients. Although sorafenib therapy offers a survival benefit, in contrast to cytotoxic chemotherapeutic agents, objective radiological tumor responses are rarely induced in the sorafenib phase II and III studies.^{[128, 129, 138]} Hence, sorafenib is generally maintained until symptomatic disease progression or deterioration in the liver or performance status of the patient, not just until radiologic tumor progression. Validated criteria to assess response or efficacy of the sorafenib therapy are required.

 

 Many agents that inhibit several molecular targets involving in hepatocarcinogenesis have been studied in phase II and III clinical trials, and some are under evaluation. Bevacizumab, a recombinant, humanized monoclonal antibody targeting VEGF, has demonstrated modest antitumor activity in phase II trials as a single agent^{[139, 140]} or in combination with erlotinib,^[141,142] cytotoxic chemotherapeutic agents capecitabine,^[143] gemcitabine and oxaliplatin (GEMOX),^[144] capecitabine and oxaliplatin^[145] in phase II studies. Sunitinib, an oral multitargeted TKI against VEGFR-1, VEGFR-2, PDGFR-a/b, c-kit, and FLt-3, had antitumor activity in four phase II HCC trials.^[146-149] A phase III open-label RCT comparing the efficacy and safety of sunitinib with sorafenib in 1073 patients, was prematurely terminated because of the severe treatment-related toxicity and the worse survival related to sunitinib treatment.^[150] Brivanib, an oral VEGFR-2 and FGFR TKI, has been shown to have antitumor activity in two phase II studies, as both first-line^[151] and second-line^[152] therapies in patients treated previously with sorafenib, with a manageable safety profile. Phase III study of brivanib versus sorafenib as a first-line therapy did not meet its primary endpoint of non-inferiority in improving OS,^[153] and in the phase III study of brivanib as a post-sorafenib second-line therapy, the median OS was better than that of placebo, but was not statistically significant (9.4 vs 8.2 months, P=0.3307).^[154] Erlotinib is a small molecule TKI associated with EGFR. Erlotinib demonstrated activity in two phase II studies with a median OS of 11-13 months.^[155,156] In a phase III trial, sorafenib plus erlotinib in combination did not improve OS or TTP over sorafenib alone.^[157] Cetuximab is a chimeric monoclonal antibody directed towards the EGFR. Cetuximab demonstrated no antitumor activity in HCC in two phase II studies.^{[158, 159]} Combinations of cetuximab with cytotoxic chemotherapies, such as gemcitabine-oxaliplatin GEMOX,^[160] and oxaliplatin-capecitabine^{[161, 162]} were evaluated in phase II studies, and were associated with modest response rates, although combination treatments were tolerable. Axitinib is a selective second generation TKI of VEGFR-1, VEGFR-2, and VEGFR-3. In the phase II trial of axitinib as second-line treatment for advanced HCC progressing after administration of TKIs/antiangiogenic drugs, a tumor control rate of 42.3% was seen at 16 weeks as the primary endpoint of manageable toxicity.^[163] OS benefit of axitinib over placebo/best supportive care was not shown in another randomized phase II trial of 202 patients who progressed or were intolerant to one prior antiangiogenic therapy (12.7 vs 9.7 months, P=0.287); however progression-free survival (PFS) and TTP favoring axitinib were significantly improved.^[164] Two phase II trials of axitinib are ongoing.^[165,166] Ramucirumab is a recombinant IgG1 monoclonal antibody acting as VEGFR2 antagonist. A phase III RCT of ramucirumab versus placebo after first-line therapy with sorafenib failed to show a significant survival benefit relative to placebo.^[167] Since a potential survival benefit was suggested in patients with a high initial level of AFP, a phase III trial of ramucirumab in patients with elevated baseline AFP has been planned.^[168] Linifanib is a selective inhibitor of the VEGFR and PDGFR. In the phase III trial of advanced HCC patients without prior systemic therapy, linifanib and sorafenib had a similar median OS of 9.1 and 9.8 months, respectively. TTP and objective response rate favored linifanib while safety results were more favorable for sorafenib.^[169] Several promising molecular targeted agents have been under various phases of clinical investigation for the treatment of HCC such as inhibitors of hepatocyte growth factor/c-Met, such as tivantinib and cabozantinib,^[170-172] mTORis SRL and EVL.^[173-175] No dominant pathway or molecular mechanism is specifically altered in HCC.^[176] A single-targeted agent may not achieve a sustained or complete response in HCC, thus combinations of effective targeted agents are also under investigation.

 

Finally, patients with terminal-stage disease (BCLC D) who have advanced liver dysfunction or cancer symptoms with major physical impairment would not benefit from the mentioned treatments above. Palliative therapies including pain and symptom management, nutrition and psychological support are the mainstay of care for these patients. RT may provide palliation for patients with painful bone metastases.

 

 

Historically, conventional external-beam RT (EBRT) has played a limited role in HCC treatment due to the risk of radiation-induced liver disease. Advances in photon RT technologies for targeting and delivering treatment such as image-guided RT, stereotactic body RT (SBRT) have facilitated dose escalation while minimizing radiation exposure to the surrounding uninvolved liver. Evidence for modern RT techniques is accumulating mainly from the studies performed in Asia, although this therapeutic option is not widely adopted in Western countries and is not a part of the treatment strategy in the BCLC algorithm.

 

SBRT is an advanced conformal EBRT technique delivering highly potent ablative radiation dose and requires stringent breathing motion management and image guidance for precise targeting. SBRT may have a complementary role to other locoregional therapies, and also may be feasible for relatively small HCC lesions that are unsuitable for surgical LR and ablative therapies. A phase II trial reported promising rates of response and local control for 50 inoperable HCC patients treated with SBRT after incomplete response to TACE; 38.3% of the patients achieved complete and another 38.3% achieved partial responses.^[177] The 2-year local control rate and OS rate were 94.6% and 68.7%, respectively.^[177] SBRT was also studied as a treatment option for advanced HCC patients with PVT.^[178]

 

Proton beam therapy (PBT) is a type of charged particle RT that allows a maximal tumor control via dose escalation while sparing surrounding structures due to the unique physical properties of the depth-dose curve. There is a growing body of efficacy evidence for proton RT particularly for patients with large tumors or portal vein involvement. In one retrospective series from Japan, 162 patients with 192 HCC lesions who had previously received some form of nonsurgical treatment were treated by PBT.^[179] 73.5% of tumors were >5 cm in diameter and 51.6% were multiple.^[179] The 5-year local control rate was 86.9% which was not different for large lesions (>5 cm).^[179] The median survival of 26.4 months was clinically noteworthy in the subgroup of 10 patients with tumor thrombus in the major branches of portal veins and very few acute and late side effects.^[179] In another large series of 242 HCC patients (12% with multiple tumors, 29% with tumors >5 cm in size, 26% with macroscopic vascular invasion, 47% with previous HCC therapy) receiving proton RT, the 5-year local control and OS rates for all patients were 90.2% and 38.0%, respectively.^[180] A benefit for local tumor control and survival is suggested with PBT in HCC patients with PVT who often need a larger volume of the liver to be irradiated with a relatively poor liver function and have limited therapeutic options.^{[181, 182]} There is a strong rationale to investigate the comparative effectiveness of different RT techniques alone and as complementary to other existing locoregional treatments in well-designed prospective randomized trials.

 

 

The investigations in the field of immunotherapy for HCC has been accelerating due to promising results obtained from trials of diverse immunotherapeutic strategies. HCC presents with multiple cellular and molecular pathways to evade antitumor immune responses, and unfortunately, the pathways to maintain the inherent tolerogenicity of the liver contribute to weaken antitumor immune responses. Several types of immunotherapeutic approaches are potentially applicable to harness the immune system and include cytokines, therapeutic vaccines, adoptive cell therapy with cytokine-induced killer cells (CIKs), immune checkpoint blockade therapy, and genetic immunotherapy.

 

Interferon have been studied as cytokine immunotherapy in HCC. In the three meta-analyses, adjuvant IFN therapy after potentially curative treatment for HCC yielded significant survival results.^[183-185] In advanced-stage HCC, IFN alpha-2b showed no benefit in terms of tumor progression rate and survival in one RCT,^[186] whereas IFN alpha-2a use was related to tumor regression and prolonged survival in another RCT.^[187]

 

Tumor vaccines are designed to enhance the intrinsic antitumor immune response against tumor-specific antigens (antigens that exclusively expressed on tumor cells), or tumor-associated antigens (antigens that are preferentially expressed on tumor cells). Glypican-3 (GPC3) is a cell surface proteoglycan which is overexpressed by most HCCs, and GPC3 immunocytochemical staining of liver biopsies plays a role in differentiation of HCC from other benign or metastatic mass lesions. In the phase I trial of GPC3-derived peptides vaccination for advanced HCC, well-tolerability, measurable immune responses, and antitumor efficacy by cytotoxic T lymphocytes infiltration of tumor, and a significant correlation of GPC3-specific cytotoxic T lymphocyte frequency with OS were noted.^[188] Telomerase activity, mainly regulated by the human telomerase reverse transcriptase (hTERT) gene, plays an important role in growth and progression of most cancers. Telomerase peptide (GV1001) vaccination binds multiple HLA class II molecules to elicit combined CD4/CD8 T-cell responses. In the phase II trial of low dose cyclophosphamide treatment in combination with GV1001 vaccination in patients with advanced HCC failed to show antitumor efficacy as tumor response and TTP.^[189] Using dendritic cells (DCs) is a promising tool for cancer vaccine development attempting to induce strong, specific T-cell responses and immunological memory to control tumor relapse through their ability of presenting tumor antigens to T cells, initiating and directing an antigen-specific immune responses, and orchestrating innate and adaptive immunity. The two widely employed vaccination strategies involving DCs are in vivo direct targeting antigens to DCs by anti-DC antibodies coupled with antigens, and ex vivo culturing autologous DCs to generate tumor antigen-bearing DCs before readministration into patients. Safe immune responses have been generated against cancer antigens in a substantial proportion of patients by DC-based vaccination,^[190-194] but the optimal vaccine design, formulation, schedule, administration strategy still remain as a challenge.

 

CIKs are an ex vivo-expanded population sharing a mixed T- and Natural killer (NK) cell-like phenotype (CD3+ and CD56+) generated from peripheral blood mononuclear cells induced by IFN-γ, anti-CD3 antibody and IL-2. Adoptive immunotherapy with CIKs has an advantageous profile by introducing a great amount of potent major histocompatibility complex (MHC)-unrestricted tumor cytolytic activity with little cytotoxicity to normal cells. There are many reports showing that CIK immunotherapy is safe, well tolerated and improves the outcomes of HCC patients. A meta-analysis of 13 RCTs including CIK therapy combined with TACE and RFA, with surgery, with TACE alone or TACE and PEI demonstrated a significant one-year and two-year survival benefit (OR=0.25, 95% CI: 0.12-0.52, P<0.001 for one-year; OR=0.17, 95% CI: 0.07-0.43, P<0.001 for two-year) in favor of CIK-based treatments.^[195] Another meta-analysis also suggested a synergistic effect of CIK therapy when combined with minimally invasive HCC treatment (after TACE or TACE plus RFA) for a longer survival.^[196] In keeping with these results, a recent randomized phase III trial showed that HCC patients who underwent surgical resection, RFA, or PEI with curative intent, CIK therapy significantly prolonged RFS and OS.^[197]

 

Immune checkpoint blockade therapy carries high expectations for HCC due to the achievements in cancers with dismal prognosis such as melanoma. It functions by monoclonal antibodies targeting the “immune checkpoints” which inhibit the immune responses by various mechanisms. The early phase studies in HCC provides preliminary evidence that antibody-based therapies targeting cytotoxic T-lymphocyte protein 4 (CTLA-4) and programmed cell death protein 1 (PD-1) demonstrated promising activity and tolerability.^{[198, 199]} A phase II study of tremelimumab (monoclonal human IgG2 antibody blocks CTLA-4 on activated T-lymphocytes) was conducted in patients with advanced HCC and chronic hepatitis C virus (HCV) infection, many with impaired liver function.^[198] The 76.4% disease control rate, and 6.4-month TTP were favorable compared with those observed in prospective clinical trials of sorafenib,^[128] and the adverse effects were acceptable.^[198] Anti-CTLA-4 and anti-PD-1 monoclonal antibodies are currently under investigation in clinical trials as a single-agent therapy or in combination strategy.^{[200, 201]} There are also additional potential immune checkpoint inhibitors like TIM-3,^[202] OX40,^[203] and CD137^[204] indicated by preclinical data.

 

 

Gene therapy involves the therapeutic transfer of genetic material (transgenes) into the target cells using a delivery system to modify their gene-expression profiles. Several studies have demonstrated the relation of genetic abnormalities with the development of HCC. The broad field of gene therapy promises various innovative applications tailored to the genetic abnormalities of HCC. Commonly used gene therapy strategies include restoration of tumor suppressor genes, genetic prodrug activating therapy, genetic immunotherapy and oncolytic virotherapy.^[205] The present gene delivery systems serving these strategies are classified as viral and non-viral gene vectors, bacteria, and physical methods. Mostly, vectors of viral origin have been used in studies because of their higher transduction efficiency, but they may be associated with cytotoxicity, immunogenicity, and high cost. The most commonly used viral vectors include lentiviruses, adenoviruses, retroviruses and adeno-associated viruses (AAV). Nonviral vector-mediated gene delivery is advantageous due to their relative safe and less immunotoxic properties, though their low transfection efficiency has limited their widespread application.

 

Approach to restore p53 function is an attractive therapeutic option in many types of cancers including HCC. The benefit of the recombinant adenovirus-mediated wild-type p53 gene (rAd-p53; trademarked as Gendicine in China) alone is controversial for HCC, though synergistic effect was observed when used in conjunction with fractionated stereotactic RT^[206] and TACE,^[207] suggesting that virally delivered tumor suppressor gene enhanced the sensitivity to RT, as p53-mediated apoptotic pathway is one of the mechanisms to explain the resistance of some tumors to radiation and apoptosis-inducing chemotherapy treatments.^[208]

 

Gene directed enzyme/prodrug therapy (GDPET), also named as suicide gene therapy, is based on the delivery of an enzyme gene to a tumor with the ability of controlled conversion of prodrugs to cytotoxic metabolites, and then administration of the prodrug in order to selectively activate a toxic effect inside the tumor site with a potent bystander effect (exhibiting an expanded toxicity to the surrounding cells). Targeted delivery of Herpes simplex virus thymidine kinase (HSV-TK) combined with the systemic administration of the prodrug ganciclovir is the most widely used gene/prodrug in HCC treatment. The HSV-TK catalyzes the phosphorylation of ganciclovir, generating toxic metabolites in the transfected cells which also exert toxic effects in the neighbor cells. This strategy was evaluated as an adjuvant treatment for HCC patients who underwent LT; adenovirus-mediated delivery of HSV-TK at the moment of LT with subsequent administration of ganciclovir was associated with an significantly increased RFS rate.^[209] Other enzyme/prodrug combinations for HCC treatment include cytochrome p450/cyclophosphamide, and yeast cytosine deaminase gene/5-fluorocytosine.

 

Cytokines have been widely evaluated with respect to the enhancement immunity to act against cancer cells. Their systemic administration is generally not accepted due to the accompanying toxicity. On the other hand, the phase I clinical trial utilizing the genetic immunotherapy approach, in which the intratumoral injection of adenoviral vector expressing interleukin 12 (Ad.IL-12) was used for advanced digestive tumors including HCC, demonstrated feasibility and safety of the procedure.^[210] Adenoviral-mediated transfer of IL-12 genes resulted in stimulation of the immune system; increased tumor infiltration by CD4+ and CD8+ T cells was observed in four of 10 patients after a single injection of Ad.IL-12.^[210] Prolonged and liver specific regulable transgene expression of IL-12 were achieved by the generation of an improved adenoviral vector containing a mifepristone (RU486)-inducible system.^[211] A potential synergistic antitumor effect was detected by the combination of vectors expressing multiple cytokines such as IL-12 with granulocyte-macrophage colony-stimulating factor (GM-CSF).^[212] An attractive alternative for genetic immunotherapy is the use of autologous DCs to improve tumor-specific immune responses. Immunization with AFP-transduced DCs were found to generate AFP-specific T-cell responses in a murine HCC model.^[213]

 

MicroRNAs (miRNAs) are small noncoding RNAs that affect many cellular pathways by regulating the expression of various target genes, and are also discovered to contribute to the cancer pathogenesis by behaving as oncogenes or tumor suppressor genes. It was demonstrated that miR-93-5p, miR-224-5p, miR-221-3p and miR-21-5p expressions were upregulated, while expressions of miR-214-3p, miR-199a-3p, miR-195-5p, miR-150-5p and miR-145-5p were decreased in the HCC compared to normal tissues.^[214] Through the accumulated evidence miRNAs represent novel potential targets for therapeutic intervention of HCC. Transfection of anti-miR-21 was shown to render HCC cells sensitive to chemotherapy with combined IFN-α and 5-FU.^[215] One study has demonstrated that miR-221 promoted liver tumorigenicity, and delivery of anti-miR-221 oligonucleotides led to reduction of the number and size of HCC nodules in the transgenic mouse model.^[216] Another study reported a link between miR122 and sorafenib sensitivity in HCC cells.^[217]

 

Oncolytic virotherapy modality is based on genetically modified viral agents that preferentially replicate in cancer cells causing their destruction. JX-594 (Pexa-Vec) is a genetically engineered oncolytic poxvirus modified by TK gene inactivation to result in increased tumor specificity and a transgene insertion that encodes GM-CSF to augment the antitumor immunity. JX-594 replicates selectively in cancer cells resulting destruction with cell-cycle abnormalities and EGFR-Ras pathway activation and achieved tumor stabilization or regression in HCC preclinical and in phase I-II clinical studies with an acceptable safety profile.^[218-220] Sequential therapy with JX-594 followed by sorafenib was associated with significantly decreased tumor perfusion, and up to 100% necrosis in three HCC patients.^[221] In contrast, a randomized phase IIb trial to determine the efficacy of JX-594 in patients who have failed sorafenib could not demonstrate an improvement in OS when compared to the best supportive care.^[222] It was concluded that JX-594 may sensitize HCC to subsequent VEGF/VEGFR inhibitor treatment and, recently a 600-patient, randomized, phase III study comparing JX-594 followed by sorafenib versus sorafenib alone (without prior sorafenib treatment) in patients with advanced HCC is planned.^[223]

 

Antiangiogenic gene therapy is an attractive approach targeting the hypervascularization of HCC which is a prerequisite for its maintenance of growth. The therapeutic potential of antiangiogenic gene therapy for HCC has been mainly demonstrated in animal models. Small interfering RNA (siRNA)-mediated knockdown of VEGF signaling was found to suppress endothelial cell proliferation in vitro and HCC growth and microvessel density in vivo.^[224] Adenoviral expression of Wnt antagonists was shown to exert antitumor activity and impair tumor vascularization.^[225] Angiogenesis inhibitor endostatin gene therapy has been intensively studied in HCC experimental studies generally combined with chemotherapeutics or other gene therapies in order to enhance the efficacy. Combined modality of recombinant AAV vector-mediated endostatin gene therapy significantly enhanced the tumor response in liver tumor mouse model.^[226] The co-expression of endostatin and soluble tumor necrosis factor-related apoptosis-inducing (sTRAIL) transgenes demonstrated antitumor activity with a reduction in tumor vessel density in mouse model.^[227] Delivery of adenoviruses encoding two antiangiogenic genes (pigment epithelium-derived factor and endostatin) in combination with two cytokines genes (GM-CSF and IL-12) was found particularly effective for large HCC in woodchuck liver.^[228] Combination of endostatin gene therapy and doxorubicin has been demonstrated to suppress tumor growth and angiogenesis, also this combination synergized to down-regulate VEGF expression in mice.^[229] In contrast to these preclinical evidence for efficacy, few antiangiogenic gene therapeutic systems have reached clinical development for HCC treatment.

 

 

Accurate assessment of tumor response is critical in measuring the efficacy of therapies and patient management. In 1981, tumor response criteria was initially proposed by WHO in an attempt to standardize the traditional tumor response assessment by bidimensional measurement of maximum tumor diameters.^[230] Subsequently, the Response Evaluation Criteria In Solid Tumors (RECIST) guidelines were introduced in 2000 by the National Cancer Institute which adopted a more simplified approach relying on the unidimensional measurement of the longest diameter of the tumor lesions for response evaluation.^[231] Nonetheless, a number of questions for these criteria appeared, leading to a revision in 2009 as RECIST 1.1.^[232] These criteria were designed with the assumption based on anatomic shrinkage of lesion as the measure of tumor activity, which is valid for anticancer cytotoxic agents. Applicability of these criteria in HCC may be suboptimal and misleading, since these criteria may not reflect reduced tumor viability or the extent of necrosis induced by successful locoregional or molecular targeted therapies which may not induce reduction in the size of the lesion. In the SHARP trial, a significant improvement in OS was demonstrated with sorafenib, despite a very low response rate of 2% by RECIST.^[128] In 2000, a panel of international experts of the EASL agreed that necrosis and reduction in viability of tumor should be considered as the optimal method to evaluate the local response for HCC.^[233] Consequently, a modification of the RECIST criteria was developed by a group of experts convened by the AASLD, and it was recommended that the sum of the diameters of residual tumor viability of the target HCC lesions recognized as the area of uptake in the arterial phase by contrast-enhanced imaging techniques should guide tumor response assessment for HCC.^[234] There is no sufficient evidence on whether newer volumetric techniques would improve the current standard of unidimensional tumor measurements allowing better assessment of therapeutic efficacy of HCC therapies and prediction of survival outcomes. The practical clinical value of these promising imaging technologies requires further clinical studies.

 

Delayed responses and initial pseudoprogression due to immunologic infiltrate rather than tumor cell proliferation were observed with immunotherapeutic agents in some solid tumors. This prompted the design of immune-related response criteria (irRC) to capture the response patterns of immunotherapy.^[235] It remains unclear whether these criteria may offer better guidance in HCC immunotherapy.

 

 

HCC is a highly prevalent and lethal malignancy, and the incidence appears to be rising in several developed countries. Most patients are diagnosed beyond the early HCC stage, when potentially curative interventions are not applicable. Treatment decisions have become increasingly complex with the availability of several therapeutic modalities and combination options for patients with each stage of disease; management is best performed with a team of specialists from different disciplines and should be individualized for each patient depending on liver function, patient and tumor characteristics. Surgery for HCC has been transforming to a minimally invasive precise LR concept with evolving technologies and sophisticated techniques. LT remains a therapeutic option with a high potential cure rate, but is precluded by the limited availability of donor organs. A debate with regard to the optimized LT criteria is still ongoing. Sorafenib remains the only approved molecularly targeted therapy, but it is likely that novel systemic agents will be developed targeting specifically the signaling pathways implicated in the hepatocarcinogenesis. Therapeutic interventions continue to evolve, but more progress is needed in the advent of novel targeted molecular therapeutics, the role of post-operative adjuvant therapies and combination treatment approaches. It is expected that preclinical evidence for efficacy of immunotherapy and gene therapy will move forward into the clinical arena. Clinical trials focusing on gene expression profiling and better characterization of the molecular basis of HCC may lead to identification of accurate prognostic biomarkers and improvement of the predictive power of the prognostic algorithmic models which may provide more individualized therapeutic decisions in the future.

 

 

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