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

Area of Science:

• Oncology
• Immunology
• Gastroenterology

Background:

• Microsatellite instability (MSI) is a key biomarker in colorectal cancer.
• Programmed death-ligand 1 (PD-L1) is an immune checkpoint target.
• Understanding PD-L1 expression patterns in MSI-high tumors is crucial for immunotherapy.

Purpose of the Study:

• To investigate PD-L1 expression patterns in MSI-high intestinal carcinomas.
• To correlate PD-L1 expression with clinicopathologic and molecular features.
• To identify potential differences in PD-L1 expression among MSI-high tumor subtypes.

Main Methods:

• Included 115 MSI-high and 41 microsatellite stable intestinal carcinomas.
• Used immunohistochemistry to assess PD-L1 expression on tumor cells and inflammatory cells.
• Correlated PD-L1 expression with histologic subtypes (medullary, mucinous, typical adenocarcinoma), MSI status, and BRAF mutation status.

Main Results:

• MSI status was significantly associated with PD-L1 expression.
• PD-L1 expression was detected on tumor cells in 28% and inflammatory cells in 77% of MSI-high tumors.
• Medullary and typical adenocarcinomas showed higher PD-L1 expression compared to mucinous adenocarcinomas.
• Increased nucleotide shifts in MSI testing correlated with higher PD-L1 expression.

Conclusions:

• PD-L1 expression patterns differ across MSI-high intestinal carcinoma histologic subtypes.
• Medullary and typical adenocarcinomas are more likely to exhibit PD-L1 expression.
• These findings may inform immunotherapy strategies for specific MSI-high tumor types.