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

Purpose: Dual PD-1/CTLA-4 inhibition shows promise in various malignancies. The SWOG S1609 Dual Anti-CTLA-4 and Anti-PD-1 Blockade in Rare Tumors (DART) trial presents initial results of ipilimumab/nivolumab in vulvar cancers. Patients and Methods: DART is a prospective/open-label/multicenter (1,016 US sites)/multicohort phase II clinical trial of ipilimumab (1 mg/kg intravenously every 6 weeks) plus nivolumab (240 mg intravenously every 2 weeks). The primary endpoint was objective response rate [ORR; confirmed complete response and partial response (PR)] per RECISTv1.1, whereas progression-free survival (PFS), overall survival, clinical benefit rate (CBR; ORR plus stable disease ≥6 months), and toxicity were 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. The ORR was 18.8% (3/16), CBR was 25% (4/16), and CBR plus unconfirmed PR rate was 31% (5/16); the PFS was 34.1, 16.7. 15.5, 7.2, and 7.0 months for these five patients, respectively. The median PFS and overall survival were 2.2 and 7.6 months, respectively. The most common adverse events were diarrhea, fatigue, pruritus, anorexia, and nausea (25%, n = 4 each). Grade 3 to 4 adverse events occurred in 25% of patients (n = 4). There was one grade 1 to 2 adverse event (6.7%) that led to discontinuation and one (6.7%) grade 5 death adverse event. Conclusions: Ipilimumab plus nivolumab in vulvar cancers resulted in an objective response in 3 of 16 patients, all of whom had durable responses lasting over 1 year. Notably, two additional patients experienced durable stable disease and unconfirmed PR. Correlative studies to determine response and resistance markers are ongoing.