Is there a correlation between clinic-pathological features, MSI, PD-L1 and survival outcomes in resected gastric cancer? Looking for optimal biomarkers.

Abstract

e15566 Background: Identification of prognostic biomarkers for gastric cancer (GC) patient selection is compelling to improve survival outcomes. Microsatellite instability (MSI) is related with a positive prognostic effect in GC, whereas perioperative chemotherapy resulted detrimental in this subgroup. In metastatic GC, immunotherapy with anti-PD1/PD-L1 drugs has shown promising results. Nevertheless, in early stages, data on the relation between MSI, clinic-pathological features, PD-L1 expression and overall survival (OS) remains sparse, especially in Western population. In our study, the prognostic role of MSI, clinic-pathological features and PD-L1 expression in a cohort of Italian GC patients was examined. Methods: CP data of 148 consecutive stage I-III GC pts resected in Cremona Institute between 2010 and 2014 (mostly chemo and/or radio-naive) were collected. MSI analysis was performed on tissue samples for all cases by polymerase chain reaction. PDL-1 expression, evaluated by immunohistochemistry, was assessed in MSI group. Differences between subgroups were evaluated with Chi-square test; Kaplan-Meier method and Long Rank test were used to calculate OS. Results: Female sex (p=0.012), earlier TNM stages (p=0.011) and limited nodal involvement (p=0.29) significantly correlated with MSI status. MSI is significantly associated with better prognosis, exhibiting an advantage of 28.6 months in OS compared with microsatellite stable subgroup (p<0.001). Most MSI patients expressed PD-L1. MSI patients without PD-L1 expression showed higher percentage of clinical features correlated with better prognosis compared with PD-L1 expressing MSI patients and MSS subgroup. Conclusions: MSI is an independent prognostic biomarker in GC and identifies a subset of patients with better OS and specific clinic-pathological features, including high percentage of PD-L1 expression. MSI could represent a promising biomarker to select patients for chemotherapy versus immunotherapy in non-metastatic disease.