BACKGROUND: Positron emission tomography (PET) is a noninvasive method to characterize different metabolic activities of tumors, providing information for staging, prognosis, and therapeutic response of patients with cancer. The aim of this study was to evaluate the feasibility of ¹⁸F-fludeoxyglucose (¹⁸F-FDG) and 3'-deoxy-3'-¹⁸F-fluorothymidine (¹⁸F-FLT) PET in predicting tumor biological characteristics of colorectal cancer liver metastasis.

METHODS: The uptake rate of ¹⁸F-FDG and ¹⁸F-FLT in SW480 and SW620 cells was measured via an in vitro cell uptake assay. The region of interest was drawn over the tumor and liver to calculate the maximum standardized uptake value ratio (tumor/liver) from PET images in liver metastasis model. The correlation between tracer uptake in liver metastases and VEGF, Ki67 and CD44 expression was evaluated by linear regression.

RESULTS: Compared to SW620 tumor-bearing mice, SW480 tumor-bearing mice presented a higher rate of liver metastases. The uptake rate of ¹⁸F-FDG in SW480 and SW620 cells was 6.07%?±?1.19% and 2.82%?±?0.15%, respectively (t?=?4.69, P?=?0.04); that of¹⁸F-FLT was 24.81%?±?0.45% and 15.57%?±?0.66%, respectively (t?=?19.99, P?<?0.001). Micro-PET scan showed that all parameters of FLT were significantly higher in SW480 tumors than those in SW620 tumors. A moderate relationship was detected between metastases in the liver and ¹⁸F-FLT uptake in primary tumors (r?=?0.73, P?=?0.0019). ¹⁸F-FLT uptake was also positively correlated with the expression of CD44 in liver metastases (r?=?0.81, P?=?0.0049).

CONCLUSIONS: The uptake of ¹⁸F-FLT in metastatic tumor reflects different biological behaviors of colon cancer cells. ¹⁸F-FLT can be used to evaluate the metastatic potential of colorectal cancer in nude mice.