A Phase II Basket Trial of Dual Anti-CTLA-4 and Anti-PD-1 Blockade in Rare Tumors (DART) SWOG S1609: Vulvar Cancers

Abstract Background: Dual PD-1/CTLA-4 inhibition shows promise in various malignancies. The SWOG S1609 DART trial presents initial results of ipilimumab/nivolumab in vulvar cancers. Methods: DART is a prospective/open-label/multicenter (1,016 US sites)/multi-cohort phase II clinical trial of ipilimumab (1mg/kg intravenously every 6 weeks) plus nivolumab (240mg intravenously every 2 weeks). The primary endpoint was objective response rate [ORR, confirmed complete and partial responses (CR and PR, respectively)] per RECISTv1.1; progression-free survival (PFS), overall survival (OS), clinical benefit rate [CBR; overall response plus stable disease (SD) ≥6 months], and toxicity are secondary endpoints. Results: Sixteen evaluable patients (median age, 55.5 years; 0-6 prior therapies; no prior immunotherapy) were analyzed, all of whom had squamous cell carcinoma histology. ORR was 18.8% (3/16), CBR was 25% (4/16), and CBR plus unconfirmed PR rate was 31% (5/16); PFS was 34.1, 16.7. 15.5, 7.2 and 7.0 months for these five patients. The median PFS and OS were 2.2 and 7.6 months. The most common adverse events were diarrhea, fatigue, pruritus, anorexia, and nausea (25%, n=4 each). Grade 3-4 adverse events occurred in 25% of patients (n=4). There was 1 grade 1-2 adverse event (6.7%) that led to discontinuation, and 1 (6.7%) grade 5 death adverse event. Conclusion: Ipilimumab plus nivolumab in vulvar cancers resulted in an objective response in three out of 16 patients, all of whom had durable responses lasting over one year. Notably, two additional patients experienced durable SD and unconfirmed PR. Correlative studies to determine response and resistance markers are ongoing.