PDCD1 and neoplasm: administration of 10 mg/BW (kg) pembrolizumab (anti-PD-1 antibody) or its control type twice a week, aspirin (10 mg/BW), SC560 (selective COX1 inhibitor, 5 mg/BW), celecoxib (selective COX2 inhibitor, 5 mg/BW), and E7046 (EP4 inhibitor, 10 mg/BW) were intraperitoneally injected three times weekly to the following tumor-bearing experimental small animal groups: B16-F10, B16-F10-NR (anti-PD-1 non-resistant), B16-F10-R (anti-PD-1 resistant), and B16-F10-R-knockout ptgs2 (B16-F10-knockout prostaglandin endoperoxide synthases/COX2).