Some time later, Krönig H. et al. [8] conducted a study on the expression of PD-1 and its interaction with PD-L1 using 100 peripheral blood samples from stage I-IV MM patients and simultaneously performed immunohistochemical reactions on 37 primary/metastatic melanoma samples, testing Melan-A, PD-L1 and PD-1. The gene discussed is CD274; the disease is metastatic melanoma.