Abstract 5189: Evaluation of thymidylate synthase mRNA expression in circulating tumor cells from non-metastatic colon and rectal patients

Abstract

Abstract Background: colorectal cancer is the third leading cause of cancer death in the United States. With different behaviors, rectal cancer represents worse prognosis, even in the locally advanced setting, with therapy following three steps, consisting of neoadjuvant chemoradiation, surgery and adjuvant chemotherapy. For non-metastatic colon cancer, the main treatment is surgery and then, patients can or not undergo adjuvant chemotherapy. Studies have shown that circulating tumor cells (CTCs) may be involved in metastatization process. Thymidylate synthase (TYMS) acts in the 5-Fluorouracil metabolism, and when overexpressed, can confer resistance to treatment, which is commonly used for neoadjuvant treatment (rectal cancer) and in combination with oxaliplatin for adjuvant treatment (colon cancer). Excision repair cross complementation Group 1 (ERCC1) is a protein involved in damage DNA repair process that is described to confer resistance to platinum-based chemotherapy. Objective: evaluate the TYMS messenger RNA (mRNA) expression in CTCs isolated from patients with locally advanced colon and rectal cancers; and its predictable value in treatment resistance. For patients with colon cancer, we also evaluated the ERCC1 protein expression in order to verify the adjuvant therapy resistance related to oxaliplatin. Methods: We collected 10 mL of blood before the beginning of treatment and processed it on ISET® (Rarecells) device. RNAscope® Technology is a novel chromogenic in situ hybridization (CISH) assay for detection of target RNA within intact cells. The expression of TYMS target gene was performed using the kit from ACDbio, as described on the protocol, but standardized to cytology. Results: there were included 12 patients of each type of tumor. We analyzed samples from 12 rectal cancer patients, and found 10 with overexpression of TYMS mRNA in CTCs. Curiously, of the two patients who had TYMSneg mRNA expression; one had complete pathological response and the other substantial down-staging. In the positive cases, 50% presented response (partial or complete) and 50% present no response and systemic progression. This result will better understood when we perform the evaluation of the protein TYMS. Among the samples from colon cancer patients, we found 8 out 12 as CTCs TYMSpos mRNA expression. Unfortunately, our recent data does not allow us to do analysis of recurrence. However, one of the positive cases had recurrence. Among the 4 TYMSneg, one had recurrence. This can be explained by the positive immunocytochemical expression of the ERCC1 protein, which confers resistance to oxaliplatin. Our next steps are to expand the CISH experiments in a larger group of patients as well as to evaluate the TYMS protein expression in the same cases. Conclusion: our preliminary results point molecular analysis of CTCs as predictor marker of colon/rectal cancer treatments. Citation Format: Bianca Troncarelli Flores, Emne Ali Abdallah, Virgílio Souza e Silva, Celso Abdon Mello, Samuel Aguiar, Renata Mayumi Takahashi, Vanessa Silva Alves, Bruna Elisa Kupper, Ludmilla T. Chinen. Evaluation of thymidylate synthase mRNA expression in circulating tumor cells from non-metastatic colon and rectal patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5189.