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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 survival (OS), clinical benefit rate (CBR; stable disease (SD) ≥6 months plus CR and PR) and toxicity.Results Sixteen evaluable patients (median age: 37) with desmoid tumors and a median of 1.5 prior therapies (with no prior exposure to immunotherapy) were analyzed. The tumors varied in location (eight abdomen, three lower limb, two upper limb, two pelvis, and one neck). ORR was 18.8% (3/16; 3 confirmed PR): 40% regression (PFS 30+ months), 83% regression (PFS 16 months) and 71% regression (PFS 8.4 months). Seven additional patients (43.8%) had prolonged SD over 6 months (PFS: 16.5, 22.4+, 22.6, 30.1, 38.2+, 48.3+ and 60.7+ months). Overall CBR was 62.5% (10/16). Median PFS was 19.4 months, with 6-month PFS of 73% and 1-year PFS of 67%. All patients were alive at 1 year; median OS was not assessable, as 13 patients were alive at analysis. Common adverse events included fatigue, nausea and hypothyroidism, with 50% experiencing grade 3–4 events. There were no grade 5 events.Conclusion Treatment with ipilimumab and nivolumab in desmoid tumors yielded an ORR of 18.8% and a CBR of 62.5% with durable responses seen. This is the first prospective study exploring the efficacy of this combination in this rare disease. Ongoing studies aim to identify markers for response and resistance. Expanded trials are necessary.Trial registration number NCT02834013.

Objectives Multiple common cancers benefit from immunotherapy; however, less is known about efficacy in rare tumors. We report the results of the adrenocortical carcinoma cohort of NCI/SWOG S1609 Dual Anti-CTLA-4 and Anti-PD-1 blockade in Rare Tumors.Design/setting A prospective, phase 2 clinical trial of ipilimumab plus nivolumab was conducted by the SWOG Early Therapeutics and Rare Cancers Committee for multiple rare tumor cohorts across >1,000 National Clinical Trial Network sites.Participants 21 eligible patients were registered. Median age was 53 years (range 26–69); 16 (76%) were women.Interventions Ipilimumab 1 mg/kg intravenously every 6 weeks with nivolumab 240 mg intravenously every 2 weeks was administered until disease progression, symptomatic deterioration, treatment delay for any reason >56 days, unacceptable or immune-related toxicity with inability to decrease prednisone to 6 months), progression-free survival (PFS), overall survival (OS), and toxicity. Immune-related outcomes included immune ORR (iORR), immune CBR (iCBR), and immune PFS (iPFS). A two-stage design was used assuming: null=5% alternative=30%, n=6 in the first stage, 16 max, one-sided alpha=13%.Results The median number of prior therapy lines was 2 (range: 1–9). 3 of 21 patients attained confirmed partial response (PR) (ORR=14%). In addition, one patient had an unconfirmed PR; one, stable disease (SD)>6 months; one, immune-related RECIST (iRECIST) PR (iPR); and one patient attained iSD>6 months: clinical benefit rate (response or SD>6 months)=5/21 (24%), iORR=4/21 (19%), iCBR=7/21 (33%). The 6-month PFS was 24%; 6-month iPFS, 33%. The PFS for patients (N=7) with iRECIST clinical benefit were 57, 52, 18, 15, 13, 7, and 7 months. The 6-month OS was 76%; the median OS, was 15.8 months. The most common toxicities were fatigue (62%) and rash (38%), and the most common grade 3/4 immune-related adverse events were hepatic dysfunction (9.5%) and adrenal insufficiency (9.5%). Treatment-related adverse events leading to discontinuation of therapy in four patients (21%). There were no grade 5 adverse events.Conclusions Ipilimumab plus nivolumab is active in refractory metastatic adrenocortical cancer meeting the primary endpoint of the study, with a 19% iORR and 33% iCBR (includes SD/iSD>6 months) and with the longest PFS/iPFS of 52 and 57 months.Trial registration number NCT02834013 (registered 15 July, 2016; https://clinicaltrials.gov/ct2/show/NCT02834013).