PURPOSE: The purpose of our retrospectively study was to evaluate the PD-L1 expression in patients with metastatic castration-resistant prostate cancer (mCRPC) treated with enzalutamide. METHODS: A total of 33 patients with mCRPC were treated with enzalutamide. All patients were previously treated by one or two lines of chemotherapy. Enzalutamide was administered in the standard dose (160 mg orally once daily as four 40 mg capsules). No corticosteroids were concomitantly administered. PD-L1 expression was determined semiquantitavely by immunohistochemistry. RESULTS: Enzalutamide was well tolerated with predominantly G1-2 toxicity. G3-4 anaemia was found in 6 patients and G3-4 thrombocytopenia in 2 patients. One patient had cerebral hemorrhage. The median progression free survival (PFS) was 7.0 months (95% CI 6.1-7.9). The median overall survival (OS) was 8.4 months (95% CI: 5.1-11.7). The shorter OS was noted in the subgroup of patients with decreasing hemoglobin levels during enzalutamide treatment with hazard ratio (HR) 0.155 (95% CI 0.053-0.449) and in patients with Gleason score 8-10 with HR 0.334 (95% CI 0.12-0.927) according to the regression analysis. All tissue samples were scored as negative in the detection of PD-L1. CONCLUSIONS: The expression of PD-L1 in prostate cancer cells as potential new predictive biomarker was not confirmed. Further studies are needed to clarify this topic.

Department of Oncology Regional Hospital Liberec Liberec Czech Republic