Understanding the Role of Molecular Testing in Endometrial Cancer

It is critical for experts who care for patients with endometrial cancer to understand the role of molecular classification in guiding treatment decisions, advocate for financial authorization of molecular tests, and request coverage for specific targeted therapies.¹

Classification and treatment of endometrial cancer have moved toward the use of molecular subtypes as providers are encouraged to universally test patients with endometrial cancer for mismatch repair deficiency (dMMR) by immunohistochemistry (IHC).

According to a practice statement published in Gynecologic Oncology, both The Cancer Genome Atlas and the ProMisE algorithm define 4 molecular subtypes of endometrial cancer, including POLE-mutated, dMMR, p53 abnormal, and no specific molecular profile.

In addition to these 4 subtypes, there are other molecular biomarkers which can influence clinical behavior and response to targeted therapies. These include beta-catenin, HER2 amplification, PI3K/mTOR/AKT alterations, L1CAM, hormone receptor expression, tumor mutational burden, and ARID1A.

Various testing strategies can be used to identify endometrial cancer biomarkers. First, IHC is performed on formalin-fixed paraffin-embedded tissue slides and antibodies are used to detect and localize antigens in tissue. IHC is used to assess dMMRstatus using mismatch repair (MMR) proteins MLH1, MSH2, MSH6 and PMS2, and is used to assess hormone receptor expression, aberrant under and overexpression of p53, and HER2 overexpression.

For microsatellite instability (MSI), a polymerase chain reaction is combined with amplification followed by capillary electrophoresis on a DNA sequencer. Newer techniques use next-generation sequencing (NGS) or multiplex PCR (polymerase chain reaction). Tumors with instability in 2 or more of the 5 analyzed markers are classified as MSI-high (MSI-H). MSI sensitivity for dMMR detection in endometrial cancer ranges from 57%-75%, meaning MSI and IHC testing can be considered.

Other tests include methylation testing, which is used in the setting of absent MLH1 or absent MLH1 and PMS2 by IHC to differentiate between somatic loss due to promoter methylation and potential germline loss; fluorescence in situ hybridization, which is used to detect amplification of ERBB2 (HER2) or CCNE1; Sanger sequencing, which is used to sequence single genes such as POLE; and NGS.

Additionally, there are a plethora of ongoing clinical trials, such as the PORTEC-4a study (NCT03469674), looking to explore treatment escalation and de-escalation within the 4 molecular subtypes. Investigators are also using clinical trials to match targeted therapies to specific mutational or biomarker profiles.

For physicians, having knowledge of patients’ MMR status is crucial in selecting second-line FDA-approved therapies for patients with recurrent endometrial cancer. In July 2021, the FDA approved the combination of pembrolizumab (Keytruda) and lenvatinib (Lenvima) for the treatment of patients with recurrent non-MSI/dMMR endometrial cancer based on findings from KEYNOTE-146/Study 111 (NCT02501096) and KEYNOTE-775 (NCT03517449). 

Additionally, pembrolizumab monotherapy was approved by the FDA for patients with recurrent MSI/dMMR endometrial cancer and tumor mutational burden–high endometrial cancer based on KEYNOTE-158 (NCT02628067) in March 2022. Following findings from the GARNET (NCT02715284) study, dostarlimab-gxly (Jemperli) also received accelerated approval from the FDA for patients with recurrent MSI-H/dMMR endometrial cancer.

Overall, the role of molecular classification is important when choosing treatment options for patients with endometrial cancer. Clinicians must understand how to guide appropriate testing, interpret results, and apply molecular information when treating patients with endometrial cancer.

REFERENCE:

1. Walsh CS, Hacker KE, Secord AA, DeLair DF, McCourt C, Urban R. Molecular testing for endometrial cancer: An SGO clinical practice statement. Gynecol Oncol. 2023;168:48-55. doi:10.1016/j.ygyno.2022.10.024