LAUSR

290Background: Atezo (anti–PD-L1) has demonstrated safety and efficacy in a broad range of cancers and is approved in the United States for mUC previously treated with platinum-based chemotherapy. Here we report long-term results in mUC from Phase Ia study NCT01375842 (PCD4989g). Methods: Previously treated mUC patients received atezo 15 mg/kg or 1200 mg IV q3w. Enrollment in this Phase Ia expansion cohort initially required PD-L1–selected status and later opened to patients regardless of PD-L1 expression on tumor-infiltrating immune cells. The primary endpoint was safety/tolerability. Secondary endpoints included investigator-assessed RECIST v1.1 ORR (confirmed), DOR and OS. Results: 95 patients were safety evaluable (Table). Median age was 66 years, 76% were male and 80% had primary bladder tumors. 61% had ECOG PS 1. 52% received ≥ 3 prior systemic therapies for mUC (70% platinum). Median treatment duration was 3 months (range: 0-32 months); 24% were treated for ≥ 1 year. Treatment-related AEs occurred ...