Expression and prognostic significance of programmed death-ligand 1 (PD-L1) in Merkel cell carcinoma.

Purpose To detect the expression of programmed death-ligand 1 (PD-L1) in Merkel cell carcinoma (MCC) and to determine the prognostic influence of the PD-L1 expression. Methods A total of 13 patients with MCC were retrospectively evaluated (12 patients with primary skin lesion, one patient was diagnosed as unknown primary MCC). All patients underwent surgical resection. PD-L1 was determinated by imunohistochemistry. Immunostaining results were evaluated semiquantitatively. The prognostic influence of the expression of PD-L1 on overall survival (OS) was calculated with the Kaplan-Meier method and log-rank test. Results PD-L1 positivity was detected in 8 patients (61.5%), in all cases the result was 1+. PD-L1 negativity was shown in the remaining 5 patients. In patients with PD-L1 positivity median OS was 42.1 months (95% CI 9.3-42.1) compared with median OS of 9.4 months (95% CI 2.1-80.9) in the group of patients without PD-L1 positivity (p=0.417). Conclusions PD-L1 positivity was found in 61.5% of patients with MCC. No prognostic significance of PD-L1 expression for OS was demonstrated.