In anti-CTLA-4 monotherapy, the incidences of both all-grade and severe diarrhea occurred most frequently in prostate cancer patients (41.9 %, 95 % CI 37.9%–47.9; 14.8 %, 95 % CI 11.5%–18.7 %, respectively). The gene discussed is CTLA4; the disease is prostate cancer.