LAUSR

381 Background: Atezo (anti–PD-L1) was the first immune checkpoint inhibitor approved for mUC. Here, we describe pt characteristics, time on tx (TOT) and distribution of tx cycles for pts receiving atezo in clinical practice, to complement data from clinical trial setting. Methods: Pts diagnosed with mUC who initiated atezo monotherapy in the first-line (1L) or second-line and beyond (2L+; prior platinum tx) settings on or before Jun 30, 2017, were identified from the US-based Flatiron Health electronic health record–derived database. Tx data were analyzed through Mar 31, 2018. TOT was defined as time from first to last atezo administration, plus 1 cycle length. Median TOT was calculated by tx line using the Kaplan-Meier method. Tx cycles were calculated by the number of atezo doses received during TOT. Corresponding results from global atezo clinical trials are presented. Results: Real-world data (RWD) from 312 pts (n = 102, 1L; n = 210, 2L+) met the study selection criteria (Table). Median TOT was 3 and 3.5 months in the 1L and 2L+ settings, respectively, with 95% CIs overlapping with the trial TOT data. A median of 4 cycles (IQR, 2-7, 1L; 2-9, 2L+) was administered in both settings. Conclusions: This is the first study of RW atezo use in mUC. The TOT with atezo observed in a US RW setting and the clinical setting (IMvigor210/IMvigor211) was similar. [Table: see text]