748P Outcomes for patients (pts) with advanced endometrial cancer (aEC) who completed pembrolizumab (pembro) and continued lenvatinib (LEN) in the phase III Study 309/KEYNOTE-775

The primary analysis of Study 309/Keynote-775 demonstrated clinically and statistically significant progression-free survival (PFS), overall survival (OS), and objective response rate (ORR) improvements in pts with aEC randomized to LEN + pembro vs chemotherapy (all-comers and pts with mismatch repair-proficient [pMMR] tumors). Pts received pembro for up to 2 yrs and continued LEN until progression or toxicity. This exploratory analysis reports outcomes in pts who completed 2 yrs of pembro and continued LEN at the final prespecified OS analysis (cutoff: 1 Mar 22). Pts with aEC and 1 prior platinum-based chemotherapy (up to 2 if 1 given in [neo]adjuvant setting) were randomized to LEN 20 mg PO QD + pembro 200 mg IV Q3W (up to 35 cycles) or chemotherapy (doxorubicin 60 mg/m2 IV Q3W or paclitaxel 80 mg/m2 IV QW [3 wks on; 1 wk off]), and stratified by MMR status (pMMR pts were further stratified by ECOG PS, geographic region, and pelvic irradiation history). We report PFS, OS, ORR, duration of response (DOR), and safety in all-comer and pMMR pts who completed 35 cycles (≈2 yrs) of pembro and continued LEN. Of 411 pts randomized to LEN + pembro (pMMR n=346), 41 (pMMR n=30) completed 35 pembro cycles, continued LEN, and are included in the analysis. Median PFS (95% CI) was 34.1 mos (20.1-not evaluable [NE]) in pMMR pts and 34.1 mos (27.7-NE) in all-comers. Median OS (95% CI) was not reached (NR [NE]) in pMMR pts and all-comers. ORR (95% CI) was 63.3% (43.9-80.1) in pMMR pts and 63.4% (46.9-77.9) in all-comers; 7 pMMR pts and 8 all-comers had a complete response. Median DOR was NR (range, 3.5-39.5+) in pMMR pts and all-comers. Grade ≥3 treatment-related adverse events occurred in 80.5% of all-comers (Table). Table: 748PpMMR pembro completers (n=30)All-comer pembro completers (n=41)Median PFSa,b (95% CI), mos34.1 (20.1-NE)34.1 (27.7-NE)Median OSb (95% CI), mosNR (NE-NE)NR (NE-NE)OS rate at 36 mosb (95% CI), %84.3 (63.2-93.8)89.0 (73.1-95.7)ORRa (95% CI), %63.3 (43.9-80.1)63.4 (46.9-77.9)CRa (95% CI), %23.3 (9.9-42.3)19.5 (8.8-34.9)Median DORa,b (range), mosNR (3.5-39.5+)NR (3.5-39.5+)Probability of pts with extended DORa, %b≥24 mos≥36 mos78.369.683.870.9Drug-related AEsc, n (%)Any gradeGrade ≥341 (100)33 (80.5)aBlinded Independent Central Review, RECIST v1.1 bProduct-limit (Kaplan-Meier) method for censored date. cReported in all-comers only. AE, adverse event; CR, complete response. Open table in a new tab aBlinded Independent Central Review, RECIST v1.1 bProduct-limit (Kaplan-Meier) method for censored date. cReported in all-comers only. AE, adverse event; CR, complete response. Ongoing clinical benefit in pembro completers who continued LEN supports LEN + pembro as standard of care in pts with aEC who received prior platinum therapy.