Background: IO combinations are standard of care for first-line therapy of clear-cell RCC; however, non-clear cell histologies including tRCC were not included in the registrational trials. We previously reported a modest efficacy (objective response rate [ORR] <20%) with IO monotherapy (PD-1 blockade) in tRCC (Boilève et al, JITC. 2018). The efficacy of IO combinations +/- VEGF TT has not been reported. Methods: This is a retrospective, international, multicenter study of pts with tRCC treated with IO-IO or IO+VEGF TT at 11 centers in the US, France, and Belgium. Only pts with confirmed TFE3 or TFEB translocation by fluorescent-in-situ hybridization (FISH) were included. ORR and progression-free survival (PFS) were assessed by RECIST. Overall survival (OS) was assessed by Kaplan-Meier methods. OS was measured from initiation of therapy till death or last follow up. We also assessed the association between OS and baseline prognostic variables. Results: 29 patients with metastatic tRCC were included in this analysis. Median age at starting therapy was 38 (IQR 27, 53) years. Female:Male ratio was 0.9:1. FISH revealed a translocation involving TFE3 and TFEB in 22 and 7 patients, respectively. Most frequent metastatic sites at diagnosis were lungs (76%), liver (52%), retroperitoneal adenopathy (48%), and bone (38%). IMDC risk at diagnosis was favorable (31%), intermediate (45%) and poor (24%). Combinations of IO+VEGF TT and anti-PD1 (L1) + anti-CTLA-4 (IO+IO) were used in 11 and 18 pts, respectively. 17 (59%) pts received IO combinations as 1L, 7 (24%) pts as 2L and 5 (17%) pts as ≥3L. ORR in the IO+IO group was 1/18 (5.5%), while in IO+VEGF TT group was 4/11 (36%). For 20 (69%) pts, progressive disease was the best overall response. At a median follow-up of 12.9 months (mo), median PFS was 3.2 mo and median OS was 13.5 mo for all 29 pts (Table). Median PFS in the IO+IO group was 2.8 mo, and 5.4 mo in IO+VEGF TT group (HR=0.81, 95% CI: 0.35-1.84). Conclusions: In this small retrospective study of tRCC, IO+IO therapy produced modest activity based on low ORR and short PFS while IO+VEGF TT produced numerically higher ORR and longer PFS. Insights into the biological basis of tRCC are necessary to develop more effective therapies for this rare and aggressive RCC variant.

*avelumab/axitinib (n=2), nivolumab/cabozantinib (n=4), pembrolizumab/axitinib (n=2), atezolizumab/bevacizumab (n=2), nivolumab/axitinib (n=1) **nivolumab/ipilimumab (n=17) and durvalumab/tremelimumab (n=1)