The Impact of Poorly Differentiated Histology on Immunotherapy in Advanced Gastrointestinal Cancers

Checkpoint inhibitors (CPI) have significantly improved survival among patients with various cancer types. Prior studies have shown a correlation between immune cell infiltration and poorly differentiated cancers. This study evaluated the impact of poorly differentiated histology on survival in patients with advanced gastrointestinal cancers treated with immunotherapy.

This study was a retrospective, single-center analysis of patients with gastrointestinal cancers treated with CPIs between 2016 and 2021. Univariate and multivariable analyses 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 and patient characteristics, progression-free survival, and overall survival.

A total of 123 patients were eligible and included in the analysis. Median age was 66 years (23-88 years). Majority had stage IV disease (89%), were white (65.5%), and were male (64.5%). Most common diagnoses were hepatocellular carcinoma (30.5%), gastric adenocarcinoma (16.5%), esophageal adenocarcinoma (17%), and colorectal cancer (19.8%). About 32% of the tumors were microsatellite instability-high (MSI-High/dMMR), with BRAF V600E mutation rate of 10%. About 25% of the patients received CPIs as initial treatment, while 35.5% had received two or more prior lines of therapy. Compared with well and moderately differentiated histology, patients with poorly differentiated tumors had a shorter median overall survival (mOS) (not reached [NR] vs. NR vs. 9.3 months, p = 0.0264). There was no statistically significant difference in median progression-free survival (mPFS) between histology types (2.5 vs. 4.2 vs. 2 months, p = 0.1314). On univariate survival analysis, moderately differentiated tumors correlated with a significantly longer mOS (HR: 0.48, CI: 0.24-0.93, p = 0.030) and mPFS (HR: 0.62, 95% CI: 0.38-1.00, p = 0.048) compared to poorly differentiated histology. Female patients (HR: 0.55, 95% CI: 0.34-0.90, p = 0.018) and the Eastern Cooperative Oncology Group (ECOG) of 1 (vs. ≥2) had significantly longer mPFS (HR: 0.58, 95% CI: 0.35-0.97, p = 0.036). ECOG of 1 also correlated with longer mOS (HR: 0.47, 95% CI: 0.23-0.94, p = 0.034). Microsatellite stable (MSS) tumors had significantly shorter mPFS (HR: 5.74, 95% CI: 2.41-13.63, p < 0.001) and mOS (HR: 5.45, 95% CI: 1.64-18.12, p = 0.006). The number of prior systemic therapies was also associated with shorter mPFS (HR: 1.19, 95% CI: 1.03-1.39, p = 0.022) and mOS (HR: 1.23, 95% CI: 1.01-1.50, p = 0.045). On multivariable analyses, ECOG status of 0/1 versus ≥2 and MSI-High/dMMR versus MSS remained significantly associated with longer mPFS and mOS. There was no correlation with histologic differentiation status, race, or mutations such as BRAF V600E or KRAS.

Results from this study demonstrate that poorly differentiated histology was associated with shorter mOS but was not associated with improved PFS in patients treated with CPI. Treatment-naïve patients, moderately differentiated tumors, female gender, ECOG 1, and MSI-High/dMMR were most likely to benefit from CPI.