Outcomes of patients (pts) with metastatic urothelial carcinoma (mUC) following discontinuation of enfortumab-vedotin (EV): Emergence of a new unmet need.

5048 Background: Enfortumab vedotin (EV) is an antibody drug conjugate recently approved to treat mUC following prior platinum and PD1/L1 inhibitors. The outcomes and patterns of therapy of pts following discontinuation of EV has yet to be studied. We investigated outcomes of pts who completed EV treatment for mUC at multiple institutions in order to identify benchmarks for evaluation of new agents following EV. Methods: Clinical data were obtained from mUC patients who had completed EV treatment from collaborating academic institutions. Descriptive stats were performed to describe the overall dataset and compare patient characteristics and outcomes of those who went on to receive further treatment post-EV and those who did not. Results: Data were available for 63 patients from 6 collaborating institutions: DFCI, University of Michigan, University of Washington, Moffitt Cancer Center, INT Milan and University of Miami. 17 (27%) were female and 46(73%) were male. The median age was 68 (range 43-83. The primary site of malignancy included bladder, upper tract, and other in 43 (68%), 19 (30%), and 1pt (.02%), respectively. The histologies included pure UC and mixed predominant UC in 49 (78%), and 14 pts (22%), respectively. 32 pts (51%) received further therapy after EV and 31pts (49%) did not. Longer duration of prior EV therapy was associated with receipt of post-EV therapy (p=0.0437). Treatments received post-EV were: trial therapy (n=14), PD1/L1 inhibitor (n=7), pemetrexed (n=4), taxane (n=3), carboplatin (n=2) and unknown in 2 pts. Objective response was observed in 3 of 32 pts (9.4%) who received therapy post-EV. The median duration of time from end of EV to death was 24 weeks. The median overall survival (OS) of those who received post-EV therapy and did not receive post-EV therapy was 37.5 weeks and 12 weeks, respectively. Conclusions: Outcomes of mUC following discontinuation of EV are dismal with only 51% receiving subsequent therapy. This study identifies an unmet need setting and establishes benchmarks for the interpretation of activity of new agents evaluated following EV.