Phase II basket trial of dual anti-CTLA-4 and anti-PD-1 blockade in rare tumors (DART) SWOG S1609: the desmoid tumors

Summary

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.