A Randomized Phase II Study of Nivolumab Monotherapy or Nivolumab Combined with Ipilimumab in Patients with Advanced Gastrointestinal Stromal Tumors

Purpose: Most gastrointestinal stromal tumors (GIST) are driven by KIT/PDGFRa mutations. Tyrosine kinase inhibitor benefit is progressively less after imatinib failure. This phase II trial analyzed the efficacy of nivolumab (N) or nivolumab + ipilimumab (N + 1) in patients with refractory GIST. Patients and Methods: Patients with advanced/metastatic GIST refractory to at least imatinib were randomized 1:1 in a noncomparative, parallel group, unblinded phase II trial of N (240 mg every 2 weeks) or N + 1 (240 mg every 2 weeks + 1 mg/kg every 6 weeks). The primary endpoint was the objective response rate of N alone or N + I by RECIST 1.1 in the intent-totreat population. Results: A total of 36 patients with a median of 3 (1-6) prior lines of therapies were enrolled. Ten of 19 (52.6%) patients had stable disease (SD) for a clinical benefit rate (CBR) of 52.6% in the N arm and the median progression-free survival (PFS) was 11.7 weeks [95% confidence interval (CI), 7.0-17.4]. In the N + I arm, 1 of 16 (6.7%) patients had a complete response (CR) and 4/16 (25.0%) had SD for a CBR of 31.3% and a median PFS of 8.3 weeks (95% CI, 5.6-22.2). The 4- and 6-month PFS were 42.1% and 26.3%, respectively for N, and 31.3% and 18.8%, respectively for N + I. The most common adverse events (AE) attributed to N and N + I were fatigue: 13.9% and 22.2%, respectively. There were nine total attributable grade 3-4 AEs. Conclusions: The primary endpoint of response rate > 15% was not observed for N or N + I. In a heavily pretreated GIST population, responses and long-term disease control with both N and N + I were observed. No new safety signals have been observed.