Nivolumab and Ipilimumab for Metastatic Castration-Resistant Prostate Cancer With an Immunogenic Signature: The Multicenter, Two-Cohort, Phase II NEPTUNES Study

PURPOSE Efficacy of immune checkpoint inhibitors in unselected patients with metastatic castration-resistant prostate cancer (mCRPC) is limited. The NEPTUNES study evaluated combination nivolumab and ipilimumab in patients with immunogenic signature–positive (ImS+) mCRPC. MATERIALS AND METHODS This open-label, 2-cohort, phase II trial enrolled patients with ImS+ mCRPC progressing on ≥1 previous line of treatment. ImS+ was defined by (1) mismatch repair deficiency (MMRD); (2) DNA damage repair gene loss; and/or (3) high inflammatory infiltrate (HII). Patients received four doses of nivolumab 1 mg/kg + ipilimumab 3 mg/kg (C1) or nivolumab 3 mg/kg + ipilimumab 1 mg/kg (C2) followed by nivolumab 480 mg once every 4 weeks up to 10 cycles. The primary end point was composite response rate (CRR) assessed radiologically, biochemically, and by reduction of circulating tumor cells. Secondary end points included toxicity, progression-free survival, overall survival, and duration of response. RESULTS Between May 2018 and June 2022, 35 (C1) and 36 (C2) patients commenced treatment. The CRR in C1 was 14/35 (40%, 90% CI, 26% to 55%) and in C2 was 9/36 (25%, 90% CI, 14% to 40%). The overall CRR was 23/71 (32%, 90% CI, 23% to 43%). Response rates were higher in patients with MMRD (7/10), BRCA2 loss (4/8), and HII ± other ImS+ features (13/30). Duration of response for patients with HII without other ImS+ features, DNA repair gene loss without MMRD, and MMRD was 2.6, 17.3, and 10 months, respectively. Grade 3 to 4 treatment-related adverse events occurred in 22/35 (63%) in C1 and 12/36 (33%) patients in C2. There were no treatment-related deaths. CONCLUSION Nivolumab 1 mg/kg + ipilimumab 3 mg/kg is an active treatment in ImS+ pretreated mCRPC. Nivolumab 3 mg/kg + ipilimumab 1 mg/kg has less toxicity but may have lower efficacy. HII is a promising prospectively tested predictive biomarker in prostate cancer that could be integrated into future trials.