Ipilimumab + nivolumab in people with rare variant renal cell carcinoma refractory to nivolumab alone: Part 2 of UNISON (ANZUP 1602) nivolumab then ipilimumab + nivolumab in advanced non-clear cell renal cell carcinoma

4565 Background: Immunotherapy targeting PD1 is active across many cancers, but many people are failed by PD1 inhibition alone. UNISON (ANZUP 1602/NCT03177239) has previously reported the activity and outcomes of nivolumab monotherapy in people with nccRCC (OTRR 17%, PFS6 45%; part 1), and here we report the outcomes of combining ipilimumab (I) and nivolumab (N), in people whose cancers are refractory to N alone (part 2). Methods: Participants (pts) with advanced nccRCC with good performance status (ECOG 0/1), were initially enrolled and took N alone. 41 pts refractory to N were offered the combination I (1mg/kg) + N (3mg/kg) every 3 weeks for up to 4 doses. Pts with disease control after N, or N + I could continue N for up to 1 year. UNISON was powered to distinguish a clinically relevant improvement in objective tumour response rate (OTRR) from 15% to 30% in people taking I+N in part 2. Results: 85 pts were enrolled and received N. 41 pts were refractory to N, were well enough to take I+N, and had a representative spectrum of nccRCC histologies (n=41; papillary 44%, chromophobe 20%, Xp11 translocation 12%, RCC unclassified 7%, other 17%). The median time on treatment was 2.1 months, the median number of doses was 3; median follow up at the time of reporting was 20.3 months. The OTRR of I+N in pts refractory to N was 10% with 1 complete and 3 partial responses. Stable disease was experienced by 36% of pts and disease progression by 52%. The disease control rate at 6 months was 45% (95% CI: 34%, 56%). The median PFS was 2.6 months (95% CI: 2.2, 3.8). The 6 month progression-free survival (PFS) was 25% (95% CI: 13-39). Only 14% of patients were free of progression at 12 months. The safety of I+N appeared similar to previous reports. 68% of pts experienced serious adverse events, 34% treatment related SAE. One pt died from refractory pneumonitis. 11 pts (27%) experienced treatment delays or permanent treatment discontinuation. Conclusions: The primary endpoint of the study was not met. A minority of pts with nccRCC refractory to nivolumab derive benefit from combination I+N but many pts remain refractory to immunotherapy. No new safety issues were identified. More effective therapeutic options are needed for people with rare variant renal cell carcinoma. Clinical trial information: NCT03177239.