Apparently, PD-1+ effector T-regs could display a major role in hyper-progressive disease (HPD) development (i.e., rapid progression of the cancer instead of its regression in certain cancer patients treated with anti-PD-1 antibody), indicating that deletion of T-regs in tumor tissues could be effective in treating HPD during anti-PD-1 mAb therapy. This evidence concerns the gene PDCD1 and cancer.