Background: Initial results of the phase 2 KEYNOTE-052 (NCT02335424) study led to approval of pembro for cisplatin-ineligible patients (pts) with advanced UC. Updated results representing follow-up of over 2 y since last pt enrolled are presented. Methods: Pts had confirmed advanced UC, were cisplatin-ineligible (ECOG PS 2, CrCl ≥30 to ˂60 mL/min, grade ≥2 neuropathy/hearing loss, NYHA Class III heart failure), and received no prior chemotherapy for metastatic disease. Pts received pembro 200 mg IV Q3W until progression, unacceptable toxicity, withdrawal, or 24 mo of therapy, whichever occurred first. Primary end point was confirmed ORR (RECIST v1.1, independent central review). Key secondary end points: duration of response (DOR), overall survival (OS), and safety. Data cutoff was September 26, 2018. Results: Among pts assessed (N = 370), median age was 74 y, 85% had visceral disease, and 30% were PD-L1 positive (combined positive score [CPS] ≥10). Median follow-up was 11.4 mo (range, 0.1-41.2) for all pts and 29.3 mo (range 7-41.2) for responders. Confirmed ORR was 29% (95% CI, 24-34): complete response, 9% (n = 33); partial response, 20% (n = 73). Median DOR was 30.1 mo (95% CI, 18.1-not reached [NR]); 67% and 52% of pts had DOR ≥12 and ≥24 mo, respectively. Median OS was 11.3 mo (range 9.7-13.1); 12- and 24-mo OS rates were 47% and 31%, respectively. In pts with CPS ˂10 (n = 251) and ≥10 (n = 110), respectively, confirmed ORR was 20% (95%CI, 16-26) and 47% (95% CI, 38-57). Median DOR for pts with CPS < 10 and ≥10 was 18.2 mo (95% CI, 9.7-NR) and NR (95% CI, 18.1-NR); DOR ≥24 mo was 45% and 57%, respectively. Median OS for pts with CPS < 10 and ≥10 was 9.7 mo (95% CI, 7.6-11.5) and 18.5 mo (95% CI, 12.2-28.5); 24-mo OS rates were 24% and 47% respectively. Treatment-related adverse events (AEs) occurred in 67% of pts. Most common were fatigue and pruritus (18% each); 21% were grade ≥3, including 1 death (myositis). Conclusions: With extended follow-up, pembro continued to elicit clinically meaningful, durable antitumor activity in cisplatin-ineligible pts with advanced UC and was more pronounced in those with PD-L1 expression CPS ≥10. Pembro safety profile was as expected. Clinical trial information: NCT02335424