Thymidylate synthase expression in circulating tumor cells: a new tool to predict 5-fluorouracil resistance in metastatic colorectal cancer patients.

Thymidylate synthase (TYMS) is an important enzyme for 5-fluorouracil (5-FU) metabolism in metastatic colorectal cancer (mCRC) patients. The search for this enzyme in circulating tumor cells (CTCs) can be a powerful tool to follow-up cancer patients. mCRC patients were enrolled before the beginning of 5-FU-based chemotherapy. The blood was filtered on Isolation by Size of Epithelial Tumor Cells (ISET), and the analysis of TYMS expression in CTCs was made by immunocytochemistry. Additionally, we verified TYMS staining in primary tumors and metastases from the same patients. There were included 54 mCRC patients and 47 of them received 5-FU-based chemotherapy. The median CTCs number was 2 per mL. We were not able to analyze immunocytochemistry in 13 samples (9 patients with absence of CTCs and 4 samples due to technical reasons). Therefore, TYMS expression on CTCs was analyzed in 34 samples and was found positive in 9 (26.5%). Six of these patients had tumor progression after treatment with 5-FU. We found an association between CTC TYMS staining and disease progression (DP), although without statistical significance (P = 0.07). TYMS staining in primary tumors and metastases tissues did not have any correlation with disease progression (P = 0.67 and P = 0.42 respectively). Patients who had CTC count above the median (2 CTCs/mL) showed more TYMS expression (P = 0.02) correlating with worse prognosis. Our results searching for TYMS staining in CTCs, primary tumors and metastases suggest that the analysis of TYMS can be useful tool as a 5-FU resistance predictor biomarker if analyzed in CTCs from mCRC patients.

Cytokeratin-based CTC counting unrelated to clinical follow up.

BACKGROUND: Circulating tumor cells (CTCs) have been reported to be a relevant prognostic biomarker in metastatic patients. However, their clinical use and impact is still under debate. We have thus comparatively and kinetically assessed two CTC detection methods according to the patient's clinical follow up. METHODS: CTC counting and characterization were repeatedly performed during follow up in a patient with metastatic undifferentiated non-small cell lung cancer by using cytokeratin (CK)-dependent immunomagnetic separation (Miltenyi) and CK-independent, size-based isolation [isolation by size of tumor cells (ISET)] (Rarecells). RESULTS: Comparison between the two methods showed a parallel increase of CTC detected by ISET and worsening of the clinical status, while CK-dependent CTC numbers were decreasing, misleadingly suggesting a response to treatment. ISET results were in agreement with the clinical follow up showing Circulating tumor microemboli (CTM) and CTC expressing a mesenchymal marker with absence of epithelial markers. CONCLUSIONS: This case report study shows the interest of a comparative and kinetic analysis of different methods for CTCs detection combined with their evaluation according to the clinical follow up. Our results should open up an area for future research and validation in larger clinical cohorts.