In NCI9673 (Part B), we evaluated the anticytotoxic T-cell lymphocyte antigen-4 (CTLA-4) antibody ipilimumab in combination with nivolumab for patients with incurable anal cancer.<h4>Methods</h4>In this phase II NCI ETCTN trial, 100 patients with refractory, incurable anal cancer were randomly assigned to receive nivolumab (480 mg IV once every 4 weeks) alone or with ipilimumab (1 mg/kg IV once every 8 weeks). The gene discussed is CTLA4; the disease is anal carcinoma.