Ipilimumab (Ipi) In Metastatic Castrate-Resistant Prostate Cancer (Mcrpc): Results From An Open-Label, Multicenter Phase I/Ii Study

25 Background: IPI is a fully human, anti-CTLA-4 monoclonal antibody capable of enhancing anti-tumor immunity. Preclinically, radiotherapy (XRT) and CTLA-4 blockade have synergistic anti-tumor activity. This phase 1/2 study in patients (pts) with mCRPC was designed to assess: safety of IPI at various doses, feasibility of combining IPI with XRT, and activity.mCRPC pts with or without prior chemotherapy were enrolled. In the dose-escalation phase, 33 pts (³6 pts per cohort) received IPI q3 weeks x 4 doses at 3, 5, or 10 mg/kg, or with XRT at 3 or 10 mg/kg. Single dose XRT (8 Gy/lesion, up to 3 lesions per pt) was given 24 to 48 h before the first IPI dose. The 10 mg/kg ± XRT cohorts were expanded to 50; 34 received IPI + XRT (Table). Based on clinical benefit, pts received additional doses of IPI. Endpoints were safety, and activity as assessed by serum prostate-specific antigen (PSA) and RECIST criteria. PSA was monitored monthly, with scans q3 months (mos).There were no dose-limiting toxicities; 10 mg/kg ± XRT cohorts were, therefore, expanded for phase 2 evaluation. Treatment-related adverse events (AEs) and immune-related AEs (irAEs) were common across all cohorts with or without XRT. Common (≥ 15%) treatment-related AEs of any grade in the 10 mg/kg ± XRT group were fatigue (50%), diarrhea (54%), nausea (24%), colitis (22%), decreased appetite (22%), vomiting (18%), rash (32%) and pruritus (20%). Most common grade 3/4 irAEs were colitis (16%), diarrhea (8%) and hepatitis (10%). irAEs were generally responsive to immunosuppressives. Of 50 PSA-evaluable pts in the 10 mg/kg ± XRT group, 8 had PSA response (Table) lasting between 3 and 13+ mos. Of the 28 tumor-evaluable pts receiving 10 mg/kg ± XRT, 1 had complete response and 6 had stable disease.In pts with mCRPC, IPI 10 mg/kg alone or in combination with XRT showed clinical antitumor activity with disease control in some patients, and a generally manageable safety profile. The combination (IPI 10 mg/kg ± XRT) and monotherapy (IPI 10 mg/kg) are being explored in randomized phase 3 trials. [Table: see text].