Introduction/Background*New/emerging therapies based on microsatellite instability (MSI) prognostic biomarker are altering the treatment landscape for advanced endometrial cancer (aEC). The real-world outcomes in aEC patients with MSI-high/deficient mismatch repair (MSI-H/dMMR) tumor status is not well understood.

Methodology Endometrial Cancer Health Outcomes (ECHO) is a multicenter retrospective chart review study in women diagnosed with aEC in the US. Physicians extracted de-identified data from medical records of women (≥18 years-old) diagnosed with inoperable aEC, with known MSI/MMR status, who progressed after prior systemic therapy between 07/01/2016-07/30/2019. Data included patient demographics, clinical/treatment characteristics, and clinical outcomes. Kaplan-Meier analyses were performed to estimate time to treatment discontinuation, real-world progression-free survival (rwPFS) and overall survival (OS). The study was IRB approved.

Result(s)*Among 130 MSI-H/dMMR aEC patients who progressed on a prior systemic therapy, mean age was 62 years, 57% had endometrioid carcinoma histology, and 93% had ECOG 0-1. As 2^nd-line therapy, 79% of patients received immunotherapy (IO) ± chemotherapy (CT) (pembrolizumab monotherapy=71%), 14% received CT only, and 7% received hormonal or other therapy (HT/OT). Median duration of 2^nd line therapy was 14 months. Median rwPFS from initiation of 2^nd-line therapy was 17 months (95% confidence interval [CI]: 13-n/a) [IO±CT: 29 months (95% CI: 18-n/a); CT: 4 months (95% CI: 2-9)]. Median OS from 2^nd-line therapy initiation was 30 months (95% CI: 18-n/a) [IO±CT: median not reached (95% CI: 30-n/a); CT: 5.5 months (95% CI: 4-n/a)]. (Table 1)

Conclusion*In real-world practice, most MSI-high/dMMR aEC patients in the US who failed a prior systemic therapy, initiated immunotherapy with favorable outcomes.