Purpose: Early phase clinical studies are ongoing to evaluate the role of immune checkpoint inhibitors in adenoid cystic carcinoma (ACC) despite a paucity of information on the immune microenvironment. This study aims to better characterize the immune microenvironment of ACC tumours and evaluate survival outcomes based on tumour infiltrating lymphocyte (TIL) and programmed death-ligand 1 (PD-L1) expression.
Methods: Patient characteristics, treatment and outcome data were collected for 24 ACC patients. The CD8+(cluster of differentiation 8) TIL and PD-L1 expression were quantified by immunohistochemistry. Marker expression and survival outcomes were evaluated by Kaplan-Meier analysis.
Results: All cases were negative for PD-L1 expression; four cases had focal high, eight cases had focal moderate and 12 cases had low TIL expression. Based on TIL expression, there was no difference in disease-free or overall survival.
Conclusion: Adenoid cystic carcinoma tumours were found to be associated with a poor immunogenic microenvironment, with absent PD-L1 expression and low CD8+ TILs. There was no association between TIL expression and survival. These data suggest that PD-L1 and TIL expression are unlikely to be useful as predictive biomarkers for response to immunotherapy.
Keywords: adenoid cystic carcinoma; PD-L1; tumour infiltrating lymphocytes.