DESCRIPTION: New therapeutic strategies for therapy-refractory metastatic urothelial carcinoma (mUC) patients are still needed. In the phase I-II ICRA trial, we evaluated whether paclitaxel plus tremelimumab (T; anti-CTLA-4), with or without durvalumab (D; anti-PD-L1), could induce a tumor response in mUC patients who had already received platinum chemotherapy and immune checkpoint inhibition (ICI). After a dose-escalation safety phase, patients were randomized between three arms: A (n=20 after expansion) paclitaxel plus T750mg (cycles 2-8); B (n=12) paclitaxel plus T300mg (cycle 2) plus D1500mg (cycles 2-13); C (n=12) T750mg (cycles 1-7). The objective response rate in arm A was 26% (88% confidence interval (CI) = [14,36%]) versus 17% (88% CI = [3,42%]) in arm B and 8% (88% CI = [0.3,33%]) in arm C. Grade 3-4 treatment-related adverse events occurred in (A) 45%, (B) 75%, and (C) 25% of patients. Murine experiments showed attenuated tumor outgrowth for paclitaxel plus anti-CTLA-4 compared to monotherapy with either agent. Transcriptomic analyses showed upregulation of inflammation signatures in on-treatment tumor tissue biopsies. This study demonstrated encouraging antitumor activity in therapy-refractory mUC treated with paclitaxel plus high-dose anti-CTLA-4 and suggests immune induction may still be possible after failure to anti-PD-(L)1 therapy. PROJECT GOAL: We aimed to explore both potential biomarkers for response to combination ICB, as well as treatment dynamics to gain a better understanding of the effects of ICB on the urothelial cancer tumor microenvironment (TME).
