Relationship Of Thymidylate Synthase Levels To Outcome Of Malignant Pleural Mesothelioma Patients Treated With Pemetrexed-Based Chemotherapy

7508 Background: Pemetrexed has shown activity in malignant pleural mesothelioma (MPM) but scanty data are available on the expression of thymidylate synthase (TS), its most important molecular target. Methods: From a database of 75 non-surgical, chemotherapy-naive MPM patients from our Institution in the period 2004–2008, 50 (male/female: 37/13, median age: 65 years) met the selection criteria i.e. epithelial type, availability of thoracoscopic tissue and outcome data. Pemetrexed was administered as single agent (14/50) or in combination with cisplatin or carboplatin (36/50). Retrospectively TS protein expression levels were evaluated by immunohistochemistry and quantified with H-score method. In addition, mRNA extraction was performed in 23 micro-dissected tissues and TS relative levels quantified by RT-PCR. Survival probability was assessed by Kaplan-Meier method and results compared by log-rank test. Cox multivariate analysis for survival was performed adjusting for clinical-pathological variables. Results: Thirty-two patients had progressive disease and 24 had died at the time of the analysis. Median time to progression (TTP) and median survival time (MST) were 11.6 and 20.9 months, respectively. Median TS H-score value was 90 (5–240). No correlation were found with sex, age, PS, stage and chemotherapy regimen. Patients with high TS H-score (4th quartile) had a significantly shorter MST (13.3 vs 21.1 months, p<0.01) and showed a trend for shorter TTP (8.3 vs 11.9 months, p=0.07). Median TS mRNA level was 1.88 (1–3.7 unit-less ratio) and a significant correlation between mRNA and protein expression (RS=0.67, p<0.0001) was found. Patients with high TS mRNA levels (4th quartile) had significantly shorter TTP (8.7 vs 14.7 months, p=0.019) and MST (11.7 vs 24.7, p=0.018). Multivariate analysis for survival indicated that TS protein levels were an independent prognostic factor (HR=2.17; CI 1.04–4.54; p=0.038). Conclusions: TS (protein and mRNA) levels predict outcome of epithelial MPM patients treated with pemetrexed-based chemotherapy. TS quantification, if confirmed in larger prospective studies, could be used to select those patients more likely to respond to chemotherapy. [Table: see text]