A phase III randomized study of adjuvant ipilimumab (3 or 10 mg/kg) versus high-dose interferon alfa-2b for resected high-risk melanoma (U.S. Intergroup E1609): Preliminary safety and efficacy of the ipilimumab arms.

9500 Background: In the U.S., 3 regimens have regulatory approval as adjuvant therapy for high-risk melanoma, including high-dose interferon-alfa (HDI) and ipilimumab 10 mg/kg (ipi10). Ipilimumab 3 mg/kg (ipi3) has regulatory approval for metastatic inoperable melanoma. The toxicity of ipi is dose- dependent, and following the recent approval of adjuvant ipi10, it has become urgent to evaluate the relative safety and efficacy of adjuvant ipi at the 2 dose levels that have been tested in E1609. Methods: E1609 randomized patients (pts) with resected high-risk melanoma (stratified by stages IIIB, IIIC, M1a, M1b) to ipi10 or ipi3 versus HDI. Co-primary endpoints were RFS and OS. The current analysis investigates the relative safety and preliminary, non-comparative RFS of the ipi arms as of 3/2/17. Results: E1609 was activated on 5/25/11 and completed adult pt accrual on 8/15/14. Accrual to ipi10 was suspended due to toxicity between 9/23-11/16/2013. Final adult pt accrual was 1670 including 511 ipi10, 636 HDI and 523 ipi3 pts. Treatment related adverse events (AEs) were reported among 503 ipi10 and 516 ipi3 pts. Worst degree (Gr 3+) AEs were experienced by 57% ipi10 and 36.4% ipi3 pts and were mostly immune related (Table 1). AEs led to discontinuation of treatment in 271 (53.8 %) of 503 ipi10 and in 180 (35.2 %) of 512 ipi3 pts during the initial 4 dose induction phase. Gr5 AEs considered at least possibly related were 8 with ipi10 and 2 with ipi3. At a median follow-up of 3.1 years, an unplanned RFS analysis of ipi3 and ipi10 on concurrently randomized pts showed no difference between the 2 arms. Three-year RFS rate was 54% (95% CI: 49, 60) with ipi10 and 56% (50, 61) with ipi3. Conclusions: Adjuvant therapy of pts with high-risk melanoma is associated with significantly more toxicity at ipi10 compared to ipi3. An unplanned RFS analysis of concurrently randomized pts on the 2 ipi arms showed no difference in RFS. Clinical trial information: NCT01274338. [Table: see text]