PD-L1 Expression Patterns in Microsatellite Instability-High Intestinal Adenocarcinoma Subtypes

OBJECTIVES: To investigate patterns of programmed death protein-1 (PD-L1) expression in microsatellite instability (MSI)-high intestinal carcinomas and correlate them with pathologic and molecular features. METHODS: One hundred and fifteen MSI-high and 41 microsatellite stable carcinomas were included. Tumor sections were immunohistochemically labeled for PD-L1. The results were correlated with histologic subtypes, MSI, and BRAF status. RESULTS: As expected, MSI status was associated with PD-L1 expression. Among 115 MSI-high tumors, PD-L1 expression was observed on tumor cells in 28 tumors and on tumor-associated inflammatory cells in 77 tumors. Medullary carcinoma demonstrated more frequent PD-L1 expression on tumor cells than mucinous and typical adenocarcinoma. PD-L1 expression was more frequent in medullary and typical adenocarcinoma than in mucinous adenocarcinoma based on combined positive scores. Tumors with more nucleotide shifts by PCR-based MSI testing were more likely to express PD-L1. CONCLUSIONS: Expression of PD-L1 is different among different histologic subtypes of MSI-high intestinal carcinomas.