Introduction/Background Recently approved therapies have proven clinical benefits for recurrent or advanced endometrial cancer (aEC) patients with known microsatellite instability (MSI) status, highlighting the prognostic significance of this biomarker. There is little information available on the prevalence of MSI/mismatch repair (MMR) testing in Europe. The objective of this study was to understand the real-world use of MSI/MMR testing in Europe.

Methodology Endometrial Cancer Health Outcomes-Europe-1st-Line (ECHO-EU5–1L) is a multicenter, retrospective, chart review study conducted in the United Kingdom (UK), France, Germany, Italy, and Spain. Physicians extracted data from medical records of female patients (≥18 years-old) diagnosed with recurrent or aEC (Stage III or IV) initiating 1st-line systemic therapy between July 1, 2016 – March 31, 2020. Data included patient demographics, MSI/MMR tumor status, and clinical/treatment characteristics. Data were de-identified before analyses. The study was IRB-approved in respective countries.

Results Of the 57 participating physicians, 94.7% were medical oncologists, 56% were in practice for ≥15 years, 96.5% practiced in urban settings, and 91.2% had hospital-based practices. The median age of 244 patients with recurrent or aEC at 1st-line therapy initiation was 69 years, 184 (75%) were White/Caucasian, and 121 (49.6%) had endometrioid carcinoma histology. A total of 88 patients (36.1%) underwent testing to determine MSI/MMR status. Prevalence of testing was 64%, 44%, 29%, 22%, and 20% in Spain, France, Germany, Italy, and the UK, respectively. Of those patients tested, 72 (81.8%) had non-MSI-high/MMR-proficient (pMMR) tumors, 13 (14.8%) had MSI-high/MMR-deficient (dMMR) tumors, and 3 (3.4%) had mixed results (table 1).

Conclusion MSI/MMR testing rates among aEC patients in Europe are low and vary across countries. The majority of tested patients had non-MSI-high/pMMR tumors. Knowledge of MSI/MMR testing may be helpful for optimal utilization of targeted therapies in Europe.