Abstract 3585
Background
The identification of prognostic biomarkers (PB) for gastric cancer (GC) patient selection is compelling to improve survival outcomes. Microsatellite instability (MSI) is related with a positive prognostic effect in resected GC, whereas perioperative chemotherapy (CT) is detrimental. In metastatic MSI GC, immunotherapy (IT) with anti-PD1/PDL-1 drugs has shown promising results. Nevertheless, in early stages (ES), data on the relation between MSI, clinic-pathological (CP) features, PDL-1 expression and overall survival (OS) remain sparse, especially in Western population. In this study, the prognostic role of MSI status, CP features and PDL-1 status in a large cohort of Italian GC patients (pts) 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 lower nodal involvement (p = 0.029) significantly correlated with MSI status. MSI is significantly associated with prolonged survival (p < 0.001), with an advantage of 28.6 months in OS compared to the microsatellite stable (MSS) group. Most MSI pts (71%) expressed PDL-1. Although not statistically significant, MSI pts without PD-L1 expression showed a better trend in OS compared with MSI GC pts expressing PDL-1 and with MSS group.Table: 688P
Main CP differences between MSS and MSI groups and survival outcomes
| MSS 110 (79.7%) | MSI 38 (25.7%) | p | |
|---|---|---|---|
| SEX M F | 77 (70) 33 (30) | 18 (47.4) 20 (52.6) | 0.012 |
| STAGE (TNM) I II III | 19 (17.3) 26 (23.6) 65 (31.6) | 13 (34.2) 13 (34.2) 12 (31.6) | 0.011 |
| NODAL METASTASES NO YES | 26 (23.6) 84 (76.4) | 16 (42.1) 22 (57.6) | 0.029 |
| OS (months) | 16.1 | 44.7 | <0.001 |
Conclusions
MSI is an independent PB in GC and identifies a subset of pts with better OS and specific CP characteristics, including high expression of PDL-1. MSI could be a promising biomarker to select pts for CT vs IT in ES of GC.
Clinical trial identification
Legal entity responsible for the study
ASST Cremona.
Funding
Has not received any funding.
Editorial Acknowledgement
Disclosure
All authors have declared no conflicts of interest.