Thymidylate synthase expression in circulating tumor cells: A new tool to predict 5‐fluorouracil resistance in metastatic colorectal cancer patients

Abstract

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 5 0.07). TYMS staining in primary tumors and metastases tissues did not have any correlation with disease progression (P 5 0.67 and P 5 0.42 respectively). Patients who had CTC count above the median (2 CTCs/mL) showed more TYMS expression (P 5 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.Colorectal cancer (CRC) was the third most commonly diagnosed cancer in both men and women in the last 3 years in the United States. 1-3 For metastatic patients, the strategy for treatment is mostly 5-Fluorouracil-based chemotherapy, which shows high efficacy in a subset of patients. However, even those patients can experience disease progression due to 5-FU resistance. 4 TYMS is a constitutive enzyme that catalyzes the reductive methylation of deoxyuridine monophosphate (dUMP) by CH 2 H 4 folate to produce deoxythymidine monophosphate (dTMP) and H 2 folate leading to DNA replication and repair. 5 An upgrade of resistance to the treatment has been often correlated to increased levels of TYMS in cancer cells. 6 Others have demonstrated that intratumoral TYMS mRNA expression levels (in paraffin-embedded tissues) are independent predictive markers of survival for 5-FU and oxaliplatin combination therapy. 7 Although the presence of high levels of TYMS presents poor outcome, it becomes hard to evaluate since there are heterogeneity among the population, methods and techniques as well. Furthermore, the best way to detect the presence of TYMS and its real value remains unclear 8 as there is not a consensus about the role of TYMS expression in mCRC published in the last 20 years. Thence, analyzing

Circulating Tumor Cells and Circulating Tumor DNA: Challenges and Opportunities on the Path to Clinical Utility

“…In patients with metastatic colorectal cancer, thymidylate synthase expression in CTCs has been studied as a potential marker of resistance to 5-fluorouracil (41). Immunofluorescent markers have been used to study androgen receptor (AR) signaling in CTCs from patients with metastatic prostate cancer to tailor hormonal treatment approaches (42).…”

E-cadherin: A potential biomarker of colorectal cancer prognosis

“…The US Food and Drug Administration has validated them as monitoring markers, as they may predict response to treatment (16). Circulating DNA is also considered as a promising type of prognostic marker.…”

MRP1 expression in CTCs confers resistance to irinotecan‐based chemotherapy in metastatic colorectal cancer

“…Reinforcing the concept of different resistance mechanisms, we previously carried out a subpopulation of this study for the presence of TYMS staining in CTCs, to associate with tumor resistance to 5‐FU agents . Interestingly, we found that none of the patients irinotecan‐resistant belonged to the population of 5‐FU resistant, indeed highlighting the different mechanisms of resistance.…”

“…In a previous study of our group, we investigated the role of Thymidylate Synthase (TYMS) expression, a protein correlated to tumor resistance to 5‐FU‐based therapy, in CTCs from patients treated with FOLFIRI/FOLFOX/5‐Fluorouracil (5‐FU). All of them received 5‐FU‐based chemotherapy, so we focused on TYMS expression.…”