Poorly differentiated histology as a predictive biomarker in patients with advanced gastrointestinal (GI) cancers treated with immunotherapy.

Abstract

664 Background: Checkpoint inhibitors (CPI) have significantly improved survival among patients with various cancer types. Prior studies have showed a correlation between immune cell infiltration and poorly differentiated cancers. We evaluated the impact of poorly differentiated histology on survival in patients with advanced GI malignancies treated with immunotherapy. Methods: We performed a retrospective, single institution analysis of patients with poorly differentiated GI tumors treated with CPI between 2016 and 2021. Univariate (UVA) and multivariable analyses (MVA) were performed to identify factors associated with patient outcome. Kaplan-Meier analysis and Cox proportional hazards models were used to assess the association between tumor/patient characteristics, progression free survival (PFS) and overall survival (OS). Results: A total of 123 patients were included. Median age was 66years. Majority had stage IV disease (88.2%), were White (65.5%) and male (64.5%). Most common diagnoses were HCC (28.5%), gastric (15.4%) and esophageal (14.6%) adenocarcinomas. About 32% were MSI-H, with 10% BRAF mutation rate. About 25% received CPI as initial treatment and 35.5% received 2 or more prior lines of therapy. Compared with well and moderately differentiated histology, poorly differentiated tumors had shorter mPFS (3.4 vs 2.5 vs. 2.2months; p = 0.29) and mOS (not reached [NR] vs. 20.9 vs. 14.2 months; p = 0.14) respectively. On UVA, the degree of tumor differentiation did not correlate with mPFS or mOS. Female patients (HR: 0.55, CI: 0.34-0.90, p = 0.018) and ECOG of 1 vs. ≥2 had significantly longer mPFS (HR: 0.58, CI: 0.35-0.97, p = 0.036). ECOG 1 correlated with better mOS (HR: 0.47, CI: 0.23-0.94, p = 0.034). Microsatellite stable (MSS) tumors had significantly shorter mPFS (HR: 5.74, CI: 2.41-13.63, p < 0.001) and mOS (HR: 5.45, CI: 1.64-18.12, p = 0.006). Number of prior systemic therapies was also associated with shorter mPFS (HR: 1.19, CI: 1.03-1.39, p = 0.022) and mOS (HR: 1.23, CI: 1.01-1.50, p = 0.045). On MVA, ECOG status of 0/1 vs. ≥2 and MSI-H vs. MSS remained significantly associated with longer mPFS and mOS. There was no correlation with race or mutations such as BRAF or KRAS. Conclusions: Poorly differentiated histology did not predict for PFS or OS. Treatment naïve patients, female gender, ECOG 1 and MSI-H were most likely to benefit from CPI.