Furthermore, a recent retrospective analysis of metastatic melanoma patients (n = 104) treated by PD-1 inhibitors demonstrated that most patients with a partial response (PR) based on the RECIST achieved CMR in 18F-FDG-PET at 1 year after initiation of treatment with a PD-1 inhibitor, and the majority of patients with CMR at 1 year exhibited continued response to treatment thereafter, suggesting the clinical utility of 18F-FDG-PET in predicting the long-term survival [35]. Here, PDCD1 is linked to metastatic melanoma.