2373P Outcomes by retrospective eligibility for maintenance therapy of patients (pts) with advanced urothelial carcinoma (UC): Post hoc analysis of KEYNOTE-361

The phase 3 KEYNOTE-361 trial (NCT02853305) of 1L pembrolizumab + chemotherapy (chemo) or pembrolizumab vs chemo alone in pts with advanced UC completed enrollment prior to approval of PD-L1 maintenance therapy after 1L chemo. This post hoc exploratory analysis evaluated pts who received chemo by eligibility for post-chemo maintenance therapy. Pts who received chemo alone were retrospectively categorized as eligible (received ≥4 cycles of chemo and either did not have PD or died within 0-10 wk after completion of chemo or did have a PD or died >10 wk after completion of chemo) or ineligible (received ≥4 cycles of chemo and had a PD or died while on chemo or within 0-10 wk after completion of chemo) for post-chemo maintenance. Pts who received <4 cycles of chemo, were censored before end of chemo, or had nonevaluable or missing scans within 10 wk of chemo were excluded. Exploratory end points were PFS, landmark PFS (time from last non-PD assessment within 0-10 wk of chemo completion to PD per RECIST v1.1 by BICR), OS, and landmark OS (time from last non-PD assessment within 0-10 wk of chemo completion to death). Median follow-up was 31.7 mo (range, 22.0-42.3). Among 342 pts in the chemo arm, 172 (50.3%) were eligible for maintenance, 108 (31.6%) were ineligible, and 62 (18.1%) were excluded; 85/172 pts (49.4%) received subsequent anti–PD-1/L1 therapy. Results for pts eligible for post-chemo maintenance are reported (Table). For maintenance-ineligible pts, median (95% CI) PFS and OS were 5.1 mo (4.2-6.0) and 10.2 mo (9.1-11.6), respectively. This post hoc exploratory analysis demonstrates that pts who are eligible for post-chemo maintenance therapy have a favorable prognosis. About 50% of pts who initiated chemo on a clinical trial were considered eligible for maintenance therapy. To our knowledge, these are the first exploratory data describing outcomes of maintenance-eligible pts from the initiation of chemo.Table: 2373PMaintenance eligible n = 172PFS, median (95% CI%), mo9.0 (8.4-10.4)PFS rate at 12 mo, % (95% CI)35.1 (27.3-43.0)Landmark PFS, median (95% CI), mo4.1 (2.9-6.1)Landmark PFS rate at 12 mo, % (95% CI)25.2 (17.9-33.2)OS, median (95% CI, mo)23.3 (19.4-26.1)OS rate at 24 mo, % (95% CI)46.8 (39.2-54.1)Landmark OS, median (95% CI), mo18.8 (14.6-21.8)Landmark OS rate at 24 mo, % (95% CI)39.9 (32.2-47.5) Open table in a new tab