Outcomes using enfortumab vedotin for metastatic urothelial carcinoma stratified by prior response to immunotherapy: A single institution experience.

77 Background: Enfortumab vedotin (EV) is a preferred systemic therapy for patients with metastatic urothelial carcinoma (mUC) who have already been treated with checkpoint inhibitor immunotherapy (IO) +/- cytotoxic chemotherapy. We examined our institution’s experience using EV to treat mUC to determine whether prior-line IO response could predict subsequent clinical outcomes on EV. Methods: Patients treated with EV for mUC at our institution were reviewed. Patient characteristics were noted, including age, sex, primary site of disease, and prior lines of treatment for mUC. Clinical responses to IO and EV were defined by best response to that line of therapy; patients were deemed to have “initial benefit” to a line of therapy if their best response was complete response (CR), partial response (PR), or stable disease (SD). Patients were deemed to have “initial resistance” to a line of therapy if their best response was progression of disease (PD). Progression free survival (OS) and overall survival (OS) were calculated from time of EV start to progression/death or death, respectively. Results: Thirty-six patients treated with EV were identified, of whom 30 had received prior IO and were included in the final analysis. The median age at time of EV start was 69.5 years, 21/30 patients were male, and 19/30 had a primary site of bladder for their (mUC). Eighteen patients (60%) had initial resistance as their best response to IO, while only 12 (40%) had initial benefit as their best response to IO (before eventually being treated with EV in a subsequent line). There were no statistical differences in OS or PFS for patients treated with EV when stratifying by prior IO response (Table). Half (15/30) of the patients had initial benefit as best response to EV, while 9/30 patients had initial resistance, and 6/30 patients were not evaluable. There was no statistically significant association between response to EV (initial benefit vs initial resistance) and response to IO as assessed by Fisher’s exact test (p=0.4). Conclusions: Patients have similar clinical outcomes on EV regardless of their responses to prior-line IO therapy. [Table: see text]