A study of thymidylate synthase gene expression as a biomarker for the treatment of esophageal adenocarcinoma.

Abstract

e15563 Background: Expression of thymidylate synthase (TS), a target of fluoropyrimidine-based (5-FU) chemotherapy, has prognostic value in colorectal adenocarcinoma. Its value as a biomarker in treatment of esophageal adenocarcinoma (EAC) is unknown. With widespread adoption of CROSS trial protocol for treatment of EAC, 5-FU is frequently omitted from regimens. We retrospectively analyzed the association between TS protein expression and clinical outcomes in EAC. Methods: TS expression levels were measured by immunohistochemistry in formalin-fixed paraffin-embedded specimens from 35 primary EAC patients from 2 institutions (range 5/2006-1/2016); at time of diagnosis and surgical resection (33 neoadjuvant chemoradiation and 2 surgery alone). TS expression higher than 1+, 5% was read as positive. Mean follow up was 1323 days (range 263-3677). TS expression correlated with treatment response and survival in patients treated with and without 5-FU therapy (log-rank test, Kaplan-Meier method). Results: In the cohort of 35 patients, 21 patients (60%) had pretreatment positive TS expression. Overall survival (OS) for TS negative patients was 1216 days versus 974 days for TS positive (p = 0.15). In the 23 patients treated with 5-FU, TS-negative patients had a trend towards longer overall survival compared to TS-positive patients, mean OS (1272 days versus 743 days, p = 0.08). In the group of 12 patients not treated with 5-FU, 2 patients showed negative TS staining. Neoadjuvant chemoradiation was performed in 33/35 patients. Downstaging was observed in 69% (9/13) of patients with negative pre-treatment TS levels versus 55% (11/20) in pre-treatment TS positive patients (p = 0.48). In 23 patients treated with 5FU, 9/12 (75%) were downstaged in the TS-negative cohort versus 6/11 (45%) in the TS-positive cohort (p = 0.21). In the 5FU treatment group, complete response was seen in 2 patients with negative TS staining. Conclusions: Low TS expression in EAC patients trended towards improved survival and tumor downstaging, particularly in patients treated with neoadjuvant 5-FU and platinum based therapy. Prospective data and greater patient numbers may be necessary to demonstrate statistical significance.