Real-world (rw) patient characteristics, treatment (tx) patterns, and clinical outcomes in advanced (adv) and recurrent (rec) endometrial cancer (EC) patients (pts) with known mismatch repair/microsatellite instability (MMR/MSI) status in Canada.

e23308 Background: Molecular characterization and treatments for adv/rec EC have evolved in recent years. Given limited biomarker-based data on EC reported in Canada, this rw study examined tx patterns and clinical outcomes in pts with adv/rec EC by MMR/MSI status. Methods: This retrospective study used de-identified patient chart data reported by Canadian physicians. Adult female pts included were diagnosed with adv (Stage III/IV) or rec (Stage I/II with advanced recurrence) EC from 01-01-2017 to 31-12-2022 with ≥2 clinical visits and underwent MMR/MSI testing. Follow-up was until 30-09-2024. Patient characteristics, tx patterns and clinical outcomes were descriptively analyzed for the overall cohort and MMR deficient (dMMR/MSI-H) and MMR proficient (pMMR/MSS) subgroups. Kaplan-Meier analyses estimated overall survival (OS) and progression-free survival (PFS) starting from first-line (1L) tx initiation. Results: 209 pts diagnosed with adv (79.4%) or rec (20.6%) EC were included. The pMMR/MSS and dMMR/MSI-H subgroups comprised of 67.5% and 32.5% of the cohort, respectively. The mean age was 63.6 years (range: 33-86), 54.5% had no comorbidities, 54.5% had BMI ≥30, 71.8% were ECOG performance status 0, and most common histology was endometrioid EC (58.9%). Only 44.0% of pts had MMR testing within 1 month of diagnosis (dx). Besides MMR, most common tested biomarkers were p53 (77.5%), estrogen receptor (73.7%) and progesterone receptor (58.4%). Of the 209 pts, 178 (85.2%) received tx, of which, 120 (67.4%) only received 1L tx. Mean duration of follow-up from 1L initiation was 30.0 months (SD: 20.0). Median time from dx to 1L was 4.1 months (IQR: 2.3-6.1). Pts spent an average of 4.0 months (SD: 4.5) on 1L and 5.8 months (SD: 5.5) on second-line (2L). Most common 1L tx among both subgroups was chemotherapy (CT) (90.2% in pMMR/MSS, 91.1% in dMMR/MSI-H) with carboplatin + paclitaxel as most common regimen. In 2L, most common tx in pMMR/MSS pts after CT (59.1%) was hormone therapy (HT) (15.9%), whereas in dMMR/MSI-H pts it was immunotherapy (IO) (50.0%) then HT (35.7%). Table shows rw survival outcomes. Conclusions: This multi-province study provides the first rw Canadian data in MMR/MSI profiled EC cohort. CT was the most common 1L tx irrespective of MMR/MSI status and in 2L, half of dMMR/MSI-H pts received IO while most pMMR/MSS pts received CT. While MMR/MSI testing is standard in Canada, faster turnaround times at dx may improve access to novel therapies, especially in pMMR/MSS pts who had slightly worse survival outcomes than dMMR/MSI-H pts. EC group n OS PFS 1 year (yr) 2 yr 3 yr 1 yr 2 yr 3 yr Overall pMMR/MSS 122 81.4% 71.5% 66.2% 62.9% 51.1% 45.1% Adv. 105 83.4% 74.3% 68.7% 67.0% 53.9% 47.3% Rec. 17 69.1% 50.4% 50.4% 35.6% 35.6% 35.6% dMMR/MSI-H 56 83.4% 75.3% 73.1% 61.1% 61.1% 58.9%