Background: Patients with advanced melanoma primarily refractory to single agent PD-1 blockade therapy have an option of receiving the CTLA-4 blocking antibody ipilimumab, but if ipilimumab should be given as a single agent or in combination with the anti-PD-1 nivolumab has not been established prospectively.

Methods: Patients aged >18 with metastatic or unresectable melanoma without objective response to anti-PD-1 therapy given without CTLA-4 therapy were randomized 3:1 to receive either ipilimumab 3mg/kg + nivolumab 1mg/kg q3 wks x4 cycles followed by nivolumab 480mg q4wks (ipi/nivo) up to 2 years, or ipilimumab 3mg/kg q3weeks x4 cycles (ipi). Additional key eligibility criteria included ECOG Performance Statue (PS) 0-2, no active central nervous system metastases, autoimmune disease, or need for steroids at doses of >10 mg of prednisone or the equivalent. The primary endpoint was progression free survival (PFS). Disease assessments were performed every 12 weeks until progression. Secondary endpoints included overall survival (OS), objective response rate (ORR), and toxicity. All patients were to submit a fresh tumor biopsy and whole blood for correlative endpoints prior to cycle 1 and again at week 5.

Results: 92 eligible patients were enrolled, 69 to ipi/nivo, 23 to ipi. Median age was 64 and 69 in the ipi/nivo and ipi arm respectively. 67% and 65% were male. 65% of patients in both arms had ECOG PS of 0. With a median follow up of 25.3 months, the hazard ratio (HR) for PFS was 0.63 (90% CI 0.41, 0.97) with a statistically significant 1-sided p-value of 0.04 favoring ipi/nivo. The 6-month PFS estimates were 34% (90% CI: 25%-44%) and 13% (4%-27%) for ipi/nivo and ipi respectively. ORR was 28% for ipi/nivo (95% CI 17%-40%) and 9% for ipi (95% CI: 3%-34%). With a median follow up of 24.4 months, 39/69 patients in the ipi/nivo arm and 12/23 patients in the ipi arm had died. 12-month OS was 63% (90% CI 52%-72%) in the ipi/nivo arm and 57% (38%-71%) months in the ipi arm. HR for OS was 0.94 (90% CI 0.54, 1.62) in favor of ipi/nivo with a p-value of 0.42. Adverse event rates were similar in both arms. One treatment related death was reported in the ipi/nivo arm due to disseminated intravascular coagulation and one treatment related death was reported in the ipi arm due to colonic perforation.

Conclusions: This is the first prospective randomized study comparing ipi/nivo to ipi alone in patients with melanoma without response to anti-PD1 therapy. Ipi/nivo was associated with improved progression free survival as compared to ipi alone. The response rate of 28% to ipi/nivo as compared to 9% to ipi alone implies that patients who do not respond to PD-1 alone can be rescued with ipi/nivo. The toxicity of combination therapy was manageable. Ipi/nivo is an appropriate standard in patients with metastatic melanoma who do not respond to single-agent PD-1 therapy. Identifier: NCT03033576

Funding: NIH/NCI grants: U10CA180888, U10CA180819, U10CA180821, U10CA180868; Other grants: SU2C-AACR-CT06-17

Citation Format: Ari M. Vanderwalde, James Moon, Kari Kendra, Nikhil I. Khushalani, Frances Collichio, Jeffrey A. Sosman, Alexandra Ikeguchi, Adrienne I. Victor, Thach-Giao Truong, Bartosz Chmielowski, David C. Portnoy, Michael C. Wu, Kenneth F. Grossmann, Antoni Ribas. S1616: Ipilimumab plus nivolumab versus ipilimumab alone in patients with metastatic or unresectable melanoma that did not respond to anti-PD-1 therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr CT013.