High dose bolus (HDB) interleukin-2 (IL2) and concurrent low dose ipilimumab followed sequentially by nivolumab in patients with advanced melanoma after failure of anti-PD1-based immunotherapy and BRAF-MEK inhibition.

9543 Background: Options are limited for patients with advanced metastatic melanoma who have disease progression following anti-PD1-based immunotherapy and BRAF-MEK inhibition (if BRAF V600 mutant). Evidence supports synergism between IL2 and CTLA4 blockade in enhancing the immunogenicity of the tumor microenvironment and therapeutic susceptibility to PD1 blockade. Methods: We conducted a phase II study of HDB IL2 in combination with LD ipilimumab followed sequentially by nivolumab in patients with advanced inoperable stage III or stage IV melanoma with progression after anti-PD1-based immunotherapy and BRAF-MEK inhibitors. Treatment consisted of up to 3 courses (One cycle is 21 days and one course is 4 cycles). HDB IL2 and concurrent ipilimumab 1 mg/kg were given during week 1 of the initial 2 cycles of each course. Nivolumab was given during week one of the 3 rd cycle of each course. Patients without evidence of disease progression (RECIST v.1.1) or limiting toxicities (CTCAE v.5) were offered additional courses of treatment. A Simon two-stage minimax design (Simon, 1989) was followed. We report the outcomes for Stage I. Results: 12 pts (5 female, 7 male) with metastatic melanoma (2M1a, 1M1b, 6M1c, 3M1d) were treated. Median age 53 years (33 – 69), 11 cutaneous (including 1 acral) and 1 mucosal primary. Tumor mutation status: 4BRAF (V600E), 2NRAS (p.Q61K), 1NF1. The median number of prior regimens for metastatic melanoma was 3 (range 1 - 5). Eight patients previously received ipilimumab as monotherapy or in combination with anti-PD1. On study, the median number of doses of IL2 was 9 during cycle 1 and 7 during cycle 2. A median of 2 doses of ipilimumab and 1 dose of nivolumab were given as part of the combination regimen. Among the 11 evaluable patients (completed 1 course of systemic therapy), the response rate was 2/11 (18.2 %; 95% CI: 2.3% – 51.8%); 1CR, 1 PR, 5 SD, 4 PD and 1 NE as best response. After a median follow up of 39 months, both responses are ongoing (at 10+ and 37+ months), median progression free survival (PFS) was 3 months and median overall survival (OS) was 18.8 months. One-year PFS and OS were 17% (95% CI: 4.7% - 59%) and 83% (95% CI: 65% - 100%), respectively. The adverse event profile was consistent with the expected toxicity profile for each agent with no increase in frequency with the combination. Conclusions: Our combination regimen was relatively safe and well tolerated and demonstrated promising efficacy in a heavily pretreated patient population passing the prespecified efficacy criteria for Simon Stage I. The study has moved into Stage II testing. Clinical trial information: NCT04562129 .