Therapies involving blockade of immune checkpoints, including PD-L1 and its receptor programmed cell death 1 (PD-1), are producing successful results for MCC.7 8 Although PD-L1 expression is considered a potential predictive biomarker for sensitivity to immune checkpoint blockade, it has become clear that the potential for prediction on the basis of PD-L1 expression is limited9 because of its heterogeneity. Here, PDCD1 is linked to Merkel cell skin cancer.