Thymidylate synthase expression as predictive biomarker of pemetrexed sensitivity in advanced cancer patients.

Abstract

11089 Background: Although a high level of thymidylate synthase (TS) expression in malignant tumours has been suggested to be related to a reduced sensitivity to the antifolate drug pemetrexed, no direct evidence for such an association has been demonstrated in routine clinical samples from patients treated with this drug. The purpose of this study was to evaluate the impact of quantitative TS expression in tumor cells as predictor of the efficacy in patients with advanced non-small cell lung cancer, small cell lung cancer (SCLC) and mesothelioma treated with pemetrexed in our institution. Methods: 54 patients were included in this study: 40 stage IV NSCLC (26 adenocarcinomas, 11 large cell, and 3 squamous cell carcinoma), 3 SCLC and 11 mesothelioma. 21 patients received platins-pemetrexed as first line NSCLC, 20 pemetrexed in monotherapy as second and further lines and 3 carboplatin-pemetrexed fo extensive disease SCLC. Total RNA was isolated by RNeasy FFPE procedure (Qiagen). The expression of TS was analyzed by RT-qPCR using appropriate mRNA specific primers and probes in LightCycler 480II platform at 45 cycles. TS levels was calibrated to expression in normal tissue. Results: From 54 cases, TS expression data were available in 32 cases, detecting overexpression in 23 (71.8%) and low expression in 9 (28.2%) patients. The response rate for patients with low TS expression was 0.63 compared with 0.15 in patients with overexpression (p=0.015). A significant benefit in time to progression was observed in patients with low expression (median TTP 12 vs. 2 months respectively, p= 0.002), whereas did not impact on overall survival (median OS 20 vs. 19 months respectively, p= 0.595). Conclusions: TS overexpression in tumor cells correlated with a reduced response to pemetrexed-containing chemotherapy and might be used as a predictive biomarker in advanced lung and mesothelioma cancer patients.