Real-world prevalence of microsatellite instability testing and related status in women with advanced endometrial cancer in the United States

Objectives: Microsatellite instability (MSI) due to a defective DNA mismatch repair (MMR) system has demonstrated increasing significance as a prognostic biomarker in solid tumors. With recent advancement in newer targeted therapies, understanding the MSI and MMR status of women with aEC can help guide treatment decisions. Limited information is available regarding prevalence of MSI/MMR testing and related status in women with aEC in real-world practice. Our objective is to assess the real-world prevalence of MSI/MMR testing and related status in women diagnosed with aEC in the US. Methods: Endometrial Cancer Health Outcomes (ECHO) study is an ongoing multicenter retrospective chart review study in women diagnosed with aEC treated at oncology practices across the US. Interim data were obtained from medical records of adult women (≥18 years) diagnosed with advanced or inoperable aEC (stages III or IV) between July 1, 2016 and December 31, 2018. De-identified patient chart data extracted by physicians included patient demographic and clinical characteristics, type of MSI/MMR testing, timing of testing in relation to treatment initiation, and test results. Women were categorized as 1) MS stable (MSS), MSI-low (MSI-L), or MMR proficient (pMMR), or 2) MSI-H or dMMR. Other ECHO study outcomes being collected include clinical outcomes, treatment patterns, and resource use. Results: Overall, 24 US physicians recruited in this study provided data for 386 women with aEC. About 66.7% physicians were medical oncologists, 33.3% were gynecologic oncologists, 70.8% physicians were males, 33.3% had practice experience ≥15 years, 87.5% practiced in an urban setting, and 58.3% had a group-based practice. The average age of women with aEC was 66.2 years (SD: 9.1), 68.1% were White/Caucasian, and 13.2% were of Hispanic origin. Amongst all women with aEC, 96.6% received an MSI test by PCR or MMR test by immunohistochemistry (IHC), with 80.7% tested before the initiation of first line of systemic therapy. Of those tested, 34.6% of women were MSI-H or dMMR and 65.4% were MSS, MSI-L or pMMR. MSH2 and MLH1 were the most frequently observed mutations in 61.2% and 59.2% of IHC tested women, respectively (Table 1). Conclusions: Our interim results show a high prevalence of MSI/MMR testing in women with aEC in clinical practice in the US, with more than 80% of the tests administered prior to treatment initiation. Among women with aEC tested for MSI/MMR, about one-third had MSI-H or dMMR tumor, and two-thirds had a tumor that was not MSI-H or dMMR (MSS, MSI-L or pMMR). This reflects real-world physician awareness of the importance of MSI testing in women diagnosed with aEC and practices conducive to adopting MSI-directed therapies. Download : Download high-res image (269KB) Download : Download full-size image