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Background

Recent therapeutic strategies for different cancer types have focused on targeting immune check-points, such as programmed death-1 (PD-1) and its ligand PD-L1. However, it was recently reported that men with castration-resistant prostate cancer did not respond to PD-1 blockade as monotherapy. The unresponsiveness could potentially be explained by low expression of PD-L1 on prostate tumor cells. This study investigated the expression of PD-L1 on tumor cells and tumor infiltrating lymphocytes (TILs) in men with primary prostate cancer.

Material and Methods

Immunohistochemical analysis of PD-L1 expression was performed in a cohort of men undergoing transurethral resection of the prostate and diagnosed with prostate cancer. The expression was evaluated in tissue microarrays from 522 patients with at least 25 years of follow-up.

Results

Only four of the 522 evaluated cases were positive for PD-L1, positivity on tumor cells were found in three of the cases, of which one case also had positivity on TILs, while a fourth case only had positivity on TILs.

Conclusion

Our data suggest that treatments targeting the PD-1/PD-L1 interaction may not be successful as monotherapy in patients diagnosed with localized prostate cancer due to low expression of PD-L1.