Background Dual inhibition using anti-programmed death-1 (PD-1) and anti-cytotoxic T-lymphocyte antigen-4 (CTLA-4) checkpoint inhibitors has proven effective in many cancers. However, its efficacy in rare solid cancers remains unclear. Desmoid tumors are ultrarare soft-tissue tumors, traditionally treated with surgery. This study reviews the first results of using ipilimumab and nivolumab in the desmoid tumor cohort of the SWOG S1609 Dual Anti-CTLA-4 & Anti-PD-1 blockade in Rare Tumors (DART) trial. Methods DART is a prospective/open-label/multicenter (1,016 US sites)/multicohort phase II trial of ipilimumab (1 mg/kg intravenously every 6 weeks) plus nivolumab (240 mg intravenously every 2 weeks) that opened at 1,016 US sites. The primary endpoint included overall response rate (ORR) defined as confirmed complete (CR) and partial responses (PR) based on Response Evaluation Criteria in Solid Tumors (RECIST) v.1.1. Secondary endpoints include progression-free survival (PFS), overall surv