Background: Avelumab* (MSB0010718C) is a fully human anti-PD-L1 IgG1 antibody being investigated in multiple clinical trials. We report safety and clinical activity of avelumab as a second-line therapy in patients (pts) with metastatic urothelial carcinoma (mUC) based on level of PD-L1 expression (NCT01772004). Methods: Pts with mUC unselected for PD-L1 expression received avelumab at 10 mg/kg Q2W by IV infusion until confirmed progression, unacceptable toxicity, or any criterion for withdrawal occurred. Tumors were assessed every 6 wks (RECIST 1.1). Best overall response rate (ORR) and progression-free survival (PFS) were evaluated. Adverse events (AEs) were graded by NCI-CTCAE v4.0. PD-L1 expression was assessed by immunohistochemistry. Results: As of 19 Mar 2015, 44 pts (30 men, 14 women) with mUC were treated with avelumab (median 13 wks [range 2-28]) and followed for a median of 3.5 mo (range 3.0-5.0). Median age was 68y (range 30-84), ECOG performance status was 0 (43.2%) or 1 (56.8%), and pts had received a median of 2 prior therapies (range 1- ≥ 4). Treatment-related treatment-emergent AEs (TR-TEAEs) of any grade occurred in 26 pts (59.1%); those occurring ≥ 10% were grade 1/2 infusion-related reactions (8 [18.2%]) and fatigue (7 [15.9%]). One pt had grade 3 asthenia. There were no treatment-related deaths. ORR was 15.9% (7 pts; 95% CI: 6.6, 30.1) with 1 CR and 6 PRs; 6 responses were ongoing at data cutoff. Stable disease (SD) was observed in 19 pts (42.3%) and disease-control rate (CR+PR+SD) was 59.1%. PD-L1 expression was evaluable in 32 pts. Using a ≥ 5% cutoff (10/32 [31.3%] were PD-L1+), ORR was 40.0% in PD-L1+ pts (4/10) vs 9.1% in PD-L1– pts (2/22; p= 0.060). PFS rate at 12 wks was 70.0% (95% CI: 32.9, 89.2) in PD-L1+ pts vs 45.5% (95% CI 22.7, 65.8) in PD-L1− pts. Conclusions: Avelumabshowed an acceptable safety profile and had clinical activity in pts with mUC. There was a trend towards higher ORR and prolonged PFS rate at 12 wks in pts with PD-L1+ mUC. Further analyses of PD-L1 expression and clinical activity of avelumab in UC are ongoing. *Proposed INN. Clinical trial information: NCT01772004