In our study, we aim to analyze the following: (1) the immunohistochemical expression of PD-L1 and IDO1 in MCC cells and intratumoral CD8+ and FoxP3+ lymphocytes, and (2) the prognostic role of tumoral PD-L1 and IDO1 expression, and intratumoral CD8+ and FoxP3+ counts. The gene discussed is IDO1; the disease is Merkel cell skin cancer.