3038 Background: Diarrhea resulting from immune activation has been associated with CTLA4 blockade. For example, in patients (pts) with stage IV melanoma receiving ipilimumab (MDX-010), a number of pts developed grade 3/4 autoimmune enterocolitis and severe diarrhea (Attia et al, 2005). In a single-dose phase I trial of CP-675,206 at doses up to 15 mg/kg in pts with solid tumors (n = 39), 9 instances of diarrhea were reported including 3 grade 3 events (Ribas et al, 2005). The incidence and severity of diarrhea was assessed in pts receiving CP- 675,206 in a large phase I/II study. Methods: An open-label phase I/II trial of CP-675,206 was conducted in pts with stage III (unresectable) or stage IV melanoma and an ECOG PS = 1. Diarrhea was assessed in pts treated at the phase II doses: 10 mg/kg monthly (Q1M) in phase I (n = 22), or 10 mg/kg Q1M (n = 44) or 15 mg/kg every 3 months (Q3M, n = 45) in phase II. Results: Medians of 3.5 doses (range, 1 to 18) at 10 mg/kg Q1M in phase I, 3 doses (range, 1 to 26) at 10 mg/kg Q1M in phase II, and 1 dose (range, 1 to 9) at 15 mg/kg Q3M were administered with 100% dose compliance. Treatment-related diarrhea was reported by 43 (39%) of 111 pts, and grade 3 diarrhea occurred in 14 (13%) pts. One patient had grade 4 colitis resulting in a colectomy. Diarrhea (all grades) occurred with similar frequency in each dose group; however, grade 3 treatment-related diarrhea occurred in 8% of pts treated with 15 mg/kg Q3M compared with 18% of pts treated with 10 mg/kg Q1M in phase I and 14% of pts treated with 10 mg/kg Q1M in phase II. Among 9 pts with an objective response, 8 experienced diarrhea (3 of which were grade 3). The majority of cases (65%) were mild to moderate in severity with a median time to onset of 51 days (range, 1 to 583 days) and resolution of 8 days (range, 1 to 182 days). More than half of pts who reported serious events of diarrhea were treated with steroids. Conclusions: Diarrhea associated with CP-675,206 was primarily mild to moderate in severity, transient, and manageable. In addition, 15 mg/kg Q3M may be better tolerated than 10 mg/kg Q1M. Ongoing clinical trials in pts with advanced melanoma will provide further information about the incidence, severity, and optimal management of diarrhea associated with CP-675,206. No significant financial relationships to disclose.
