© 2013, Hepatobiliary Pancreat Dis Int. All rights reserved.

doi: 10.1016/S1499-3872(13)60073-9

Contributors: All authors contributed to the design and interpretation of the study and to further drafts. ZYP 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 article.

 

 

 

 

(Hepatobiliary Pancreat Dis Int 2013;12:458-464)

 

KEY WORDS: cancer diagnosis; K-ras; pancreatic carcinoma; meta-analysis

Pancreatic carcinoma, so called "silent killer", is the sixth leading cause of cancer death in China.^[1] Surgical resection and adjuvant treatment may improve survival; however, the outcome is far from satisfactory.^[2] Its poor prognosis is mainly due to the failure of diagnosis at the early stage. Although radiological imaging techniques have been greatly advanced, early diagnosis of pancreatic carcinoma remains a challenge, especially in the setting of chronic pancreatitis. Due to its insidious onset, pancreatic carcinomas are almost always in advanced stage when diagnosed. Some serum tumor markers, such as carbohydrate antigen (CA) 19-9 or carcinoembryonic antigen (CEA), are elevated in pancreatic carcinoma; however, their sensitivity and specificity are very low. Using primer-mediated, mutant-enriched, polymerase chain reaction-restriction fragment length polymorphism analysis, Hruban and colleagues found that the K-ras gene mutation occurs frequently in adenocarcinomas of the pancreas.^[3]

 

K-ras is a member of the Ras gene family and plays a key role in Ras/mitogen-activated protein kinase signaling. Somatic mutation in K-ras can be found frequently in many cancers, pancreatic cancer is one of them. K-ras codon 12 mutation is one of the earliest genetic changes in the process of pancreatic carcinoma development and accurate detection of K-ras mutations is pivotal to molecular diagnosis.^{[4, 5]} However, the role of K-ras mutation in the diagnosis of pancreatic carcinoma remains controversial. Therefore, a large and multicenter study or a meta-analysis may help to validate the true value of K-ras mutation on the diagnosis of pancreatic cancer. The present meta-analysis was to probe the diagnostic accuracy of K-ras mutation in pancreatic carcinoma.

 

 

A systemic search of relevant literature including Web of Science, EMBASE, Cochrane Database, and MEDLINE (PubMed as the search engine) was performed to identify eligible studies prior to June 1, 2011. The related articles in PubMed and the references of identified articles were also included. Titles and abstracts were initially screened, and then the potentially included articles were evaluated by three reviewers (Liu SL, Chen G and Zhao YP). Disagreements were resolved by discussion and consensus. The search strategy was based on the combination of "ras", "pancreatic tumor/cancer/adenocarcinoma/neoplasm" and "sensitivity/specificity". Studies were considered eligible if they: (1) provided both the sensitivity and specificity of K-ras mutation for diagnosing pancreatic carcinoma; (2) contained sufficient data to calculate the diagnostic test results; (3) included more than 10 cases because small sample size may be vulnerable to selection bias; and (4) were published in English. The publications with possible overlap were discussed by the above three reviewers and only the most scientifically designed study was included. Conference abstracts were excluded because of the limited information. We also excluded basic research studies and review articles.

 

Studies fulfilling the inclusion criteria were used for data extraction. Two reviewers (Liu SL and Chen G) independently extracted the data which included authors, year of publication, test method, sample, sensitivity and specificity, as well as quality score. The methodological quality of included studies was assessed based on the guidelines published by Standards for Reporting Diagnostic Accuracy (STARD, maximum score 25) and Quality Assessment for Studies of Diagnostic Accuracy (QUADAS, maximum score 14).

 

Guidelines for meta-analysis of diagnostic studies have been used in previous publications.^{[6, 7]} STATA version 10 (STATA Corporation, College Station, TX, USA), Meta-Disc (Zamoral J, Muriel A, Abraira V. Meta-Disc for Windows, XI Cochrane Colloquium. Barcelona, 2003) and SPSS version 16.0 were used for statistical analysis. Sensitivity, specificity, positive likelihood ratio (PLR), negative likelihood ratio (NLR) and diagnostic odds ratio (DOR) in each study were calculated. A meta-analysis of sensitivity, specificity, PLR and NLR was performed by pooling data from all data series. A random-effects model was used to calculate the above measures of test accuracy.

 

 The meta-analysis was based on a summary receiver operating characteristic (SROC) curve described by Littenberg and Moses.^[8] The Chi-square test and Fisher's exact test were used to detect heterogeneity among studies and to evaluate the degree of variability. Univariate meta-regression analysis was performed to assess the effects of STARD and QUADAS scores on the diagnostic ability of K-ras mutation. The relative DOR (RDOR) was calculated to analyze the change in diagnostic precision in the study per unit increase in the covariate. The potential presence of publication bias was measured by funnel plots and Egger test.^[9] Statistical hypotheses (two-tailed) were tested at the level of 5% significance.

 

 

In 263 publications, 221 studies were excluded because they were irrelevant to the present analysis. The number of 4 of the remaining 42 articles were excluded because they analyzed the role of K-ras mutation in non-pancreatic carcinoma,^[10-13] and another four were excluded because there were insufficient information to calculate the sensitivity and specificity.^[14-17] Thirty-four studies were finally identified for the meta-analysis.^[18-51] The characteristics of these studies, along with STARD and QUADAS scores, are outlined in Table 1.

 

The total number of patients enrolled in the studies was 2687, ranging from 19 to 358 per study, only eight studies had more than 100 cases, and six studies less than 30 cases. Of the 34 studies, 13 had STARD scores ≥13 and 26 had QUADAS scores ≥10.

 

Fig. 1 shows the forest plot of the sensitivity and specificity of the included studies. The range for sensitivity was 0.20-0.94 (mean 0.68, 95% CI: 0.66-0.71), and for specificity, 0.64-1.00 (mean 0.87, 95% CI: 0.85-0.88). The PLR was 4.54 (95% CI: 3.47-5.94) and the NLR, 0.37 (95% CI: 0.30-0.44). The DOR is a number that combines the information from sensitivity and specificity into a single indicator, with higher values indicating higher diagnostic accuracy. In the present meta-analysis, DOR for K-ras mutation was 14.90 (95% CI: 10.02-22.15). Q values of sensitivity, specificity, DOR, PLR and NLR were 169.17, 112.97, 69.94, 71.80 and 185.82, respectively, with the values of the Chi-square test <0.001, indicating a significant heterogeneity among the included studies.

 

We stratified the analysis by specimen types. The pooled diagnostic sensitivity for blood analysis was 0.37 (95% CI: 0.27-0.48) and specificity was 0.91 (95% CI: 0.82-0.97); PLR was 4.02 (95% CI: 1.81-8.95), NLR was 0.70 (95% CI: 0.56-0.88) and DOR was 6.16 (2.38-15.96). The sensitivity for pancreatic cyst fluid analysis was 0.64 (95% CI: 0.44-0.81) and the specificity was 0.93 (95% CI: 0.83-0.98); PLR was 6.28 (95% CI: 2.40-16.40), NLR was 0.45 (95% CI: 0.17-1.18) and DOR was 18.34 (95% CI: 3.71-90.70). For pancreatic juice, the sensitivity was 0.57 (95% CI: 0.50-0.64) and the specificity was 0.84 (95% CI: 0.81-0.87); PLR was 2.87 (95% CI: 1.98-4.17), NLR was 0.55 (95% CI: 0.41-0.74) and DOR was 6.05 (95% CI: 3.21-11.42). For pancreatic tissue, the sensitivity was 0.74 (95% CI: 0.71-0.77) and the specificity was 0.87 (95% CI: 0.85-0.90); PLR was 6.21 (95% CI: 4.17-9.26), NLR was 0.29 (95% CI: 0.24-0.35) and DOR was 21.97 (95% CI: 14.66-32.92) (Table 2).

 

The SROC curve was constructed from original values of sensitivity and specificity. The true positive against false positive rates are shown in Fig. 2. The sensitivity in 10 (29.4%) of the 34 studies was >0.80 and in 8 studies (23.5%), the sensitivity was <0.50. In contrast, the specificity in 27 studies (79.4%) was >0.80. Our data showed that the maximum joint sensitivity and specificity was 0.79, and the overall area under the curve (AUC) for K-ras mutation was 0.86.

 

Of the available studies, RDOR, which was produced by higher quality studies and the lower ones (cut-off of STARD scores: 13), was not significantly different (P=0.890). The coefficient and RDOR were 0.065 and 1.07 (95% CI: 0.41-2.76) respectively. QUADAS, either ≥10 or <10 had no impact on diagnostic accuracy. The coefficient and RDOR were -0.391 and 0.68 (95% CI: 0.21-2.18), respectively (P=0.500). These results indicated that the study quality did not influence the accuracy of K-ras mutation in the diagnosis of pancreatic carcinoma.

 

The funnel plot for publication bias was asymmetric (Fig. 3). The evaluation showed that the Egger test was significant (P=0.006), indicating a potential publication bias.

 

 

Even though pancreatic carcinoma is virtually fatal, some of the patients might be cured if they were diagnosed early enough. K-ras mutation is an early and essential molecular event in the pathogenesis of pancreatic carcinoma. However, the accuracy of K-ras mutation in the diagnosis of pancreatic carcinoma is controversial. The present meta-analysis was to assess the diagnostic value of K-ras mutation in pancreatic carcinoma. The results indicated that the K-ras mutation had a low sensitivity and NLR, suggesting that patients with negative K-ras mutation cannot role out pancreatic carcinoma. A PLR of 4.54 indicates that patients with pancreatic carcinoma have a nearly five fold chance of K-ras mutation compared with those without pancreatic carcinoma. The DOR value for K-ras mutation was 14.90 (95% CI: 10.02-22.15), suggesting that K-ras mutation could be useful in diagnosis of pancreatic carcinoma. The diagnostic precision of K-ras mutation in pancreatic carcinoma is similar to that of conventional methods, such as CA19-9 and CEA, with a low sensitivity and a high specificity. K-ras mutation can be found in pancreatic juice, bile, blood and stool. The collection and storage of specimens, the assay techniques, and the included population can contribute to the variety of K-ras mutation. It has been reported that K-ras mutation even occurs in premalignant or normal cells.^[52] Unlike the conventional tests (CA19-9 and CEA), which are usually used as tumor markers for the general population, the assay for K-ras mutation is specifically for the patients with pancreatic diseases, including those with chronic pancreatitis and pancreatic cystic diseases. Thus, there is a huge difference between K-ras mutation and conventional assays in the diagnosis of pancreatic cancer.

 

Diagnostic accuracy of K-ras analysis for pancreatic cancer is diverse in different samples. The overall specificities in blood, cyst fluid, pancreatic juice and pancreatic tissue for diagnosing pancreatic cancer were more than 0.80, suggesting a potential role of these samples for K-ras analysis in diagnosing pancreatic cancer. The sensitivities in the four samples are, however, quite low and are more variable than specificities (from 0.37 to 0.74). The diagnostic role of K-ras analysis seems to be better in pancreatic tissue and cyst fluid than that in blood and pancreatic juice. SROC analysis also demonstrates that K-ras analyses in pancreatic tissue and cyst fluid are more sensitive and specific than that in blood and pancreatic juice.

 

In the present meta-analysis, STARD and QUADAS scores were used to evaluate the effect of study quality on diagnostic performance. The results indicated that study quality was not associated with K-ras mutation in the diagnosis of pancreatic carcinoma.

 

The present study may provide some information about the role of K-ras mutation in the diagnosis of pancreatic carcinoma. However, some limitations of this study should not be ignored. First, the excluded conference abstracts and non-English language studies may have contributed to publication bias. Moreover, some studies might have been missed, even though we attempted to include all related studies. Second, different K-ras analysis systems also affect the diagnostic accuracy. Even in the same population, the diagnostic results may be different if the K-ras analysis systems are different. In the present meta-analysis, the effect of factors such as laboratory infrastructure and the technology of K-ras mutation detection on the accuracy of meta-analysis results were not evaluated because of lack of necessary data in the original studies.

 

In conclusion, based on our meta-analysis, we cannot recommend K-ras mutation alone for the diagnosis of pancreatic carcinoma. K-ras mutation might be useful as an additional (second) assay for some patients with pancreatic tumors (cystic and solid) to contribute to cancer diagnosis. Finally, the results of this meta-analysis should be interpreted in parallel with clinical findings.

 

 

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