PDCD1 and cancer: Colitis occurs more frequently with CTLA-4 inhibitors than with PD-1 and PD-L1 inhibitors, with combination therapy with two ICPIs, and with higher doses, although a clear dose-dependence of the occurrence and severity of colitis has not been confirmed.3 The incidence of colitis is 3.4–22% with CTLA-4 inhibitor therapy, 0.7–12.8% with combined CTLA-4 and PD-1 inhibitor therapy, and 0.7–2.6% with PD-1/PD-L1 inhibitor monotherapy.1,2 Another important factor is cancer itself.