Strong PD-L1 expression in granulomatous prostatitis.

Abstract

The expression of programmed cell death ligand protein (PD-L1) is weakly investigated in non-tumoral and inflammatory prostatic pathology. The diagnosis of granulomatous prostatitis (GP) rests on the recognition of localized or diffuse epithelioid granulomatous inflammation in prostatic tissue which is frequently difficult by conventional histological observation alone. PD-L1 expression in GP is not well studied so far. We studied PD-L1 expression in 17 GP cases (9 nonspecific GP, 5 Bacillus Calmette-Guérin induced prostatitis, 1 prostatic tuberculosis, and 3 cases of postsurgical prostatic granulomas). The control group included 10 radical prostatectomies of patients with high Gleason score prostate adenocarcinoma (PCa) and National Institutes of Health-category IV prostatitis (high-grade histologic prostatitis; HG-HP). All of the GP cases showed easily visible strong membranous PD-L1 expression (high levels of combined positive score) in localized and diffuse epithelioid granulomatous prostatic inflammation. None of the control cases showed the presence of significant PD-L1 expression in inflammatory infiltrates in HG-HP, tumor parenchyma, and stroma in PCa. The study presents the first attempt to examine PD-L1 expression in GP. Granulomatous inflammation in GP is easily identified when stained with PD-L1.