Impact of DNA mismatch repair status on prognosis of patients with locally advanced gastric cancer in a Mexican population.

Abstract

408 Background: Gastric cancer (GC) is among the five most frequent and mortal cancers in the world. In Mexico, GC is the second cause of death from cancer in men between 30 and 59 years old. The role of deficient DNA mismatch repair (dMMR)/microsatellite instability-high (MSI-H) in locally advanced gastric cancer (LAGC) is still controversial. We aimed to evaluate the overall survival (OS) of patients with LAGC, according to MMR status and treatment. Methods: Retrospective study included patients from the National Cancer Institute of México, with locally advanced gastric adenocarcinoma diagnosis between 2008 and 2017. The Kaplan Meier, Log Rank, and Cox Regression methods were used to analyze the relation between MMR status and overall survival in LAGC. MMR status was assessed using immunohistochemistry. Results: A total of 103 patients with LACG were enrolled for analysis. The prevalence of dMMR in GC was 13.59% (n=14). The median OS was 101.9 months in the dMMR group vs. 86.2 months in the proficient MMR (pMMR) group (HR 0.54, 95% CI 0.19 - 1.52, p=0.23), with a 3-year OS of 71.4% vs 65.1% respectively. Survival was also analyzed according to MMR status and choosing treatment. OS was 106.8 months in the dMMR surgery alone group, 78.4 months in the dMMR group treated with both surgery and chemotherapy, 33.1 months for pMMR group with surgery alone, and 89.2 months in the pMMR group treated with surgery plus chemotherapy (p=0.014). Conclusions: In this analysis, OS tended to improve in dMMR group. pMMR surgery alone patients had a superior OS than other groups, while adding chemotherapy to surgery treatment seems to have a role only in pMMR patients. [Table: see text]