PDCD1 and cancer: Moreover, it is clinically enigmatic that a large percentage of advanced PCa cases recur after initial androgen deprivation therapy (ADT), with enhanced risk of progressing to lethal metastatic CRPC; and while immune checkpoint inhibition with anti-CTLA4 or anti-PD1/PDL1 elicits durable response/remission in many cancer types, there is accruing evidence it does not in advanced PCa, metastatic CRPC inclusive [36,37].