Prevalence of DNA Mismatch Repair Deficiencies in Multiple Solid Tumor Types in China.

[AIM] Microsatellite instability (MSI) as a result of deficient deoxyribonucleic acid (DNA) mismatch repair (dMMR) is a key contributor to the development of tumors with a high mutation rate and cancer-specific neoantigens. dMMR identification can be beneficial for selection of immune checkpoint inhibitor (ICI) therapy-eligible patients. While multiple studies have focused on dMMR prevalence in colorectal cancer (CRC), fewer investigate the prevalence of dMMR in tumor types besides CRC, especially in Chinese patients. In this study, we aimed to determine the prevalence of dMMR in China across five gastrointestinal and gynecological tumor types.

[METHODS] Tissue samples from Chinese patients with advanced endometrial, ovarian, cervical, biliary tract, or gastric metastatic or unresectable solid tumors were tested for dMMR status using immunohistochemistry with the Ventana MMR RxDx panel. Data were analyzed to determine the prevalence of dMMR for each tumor type.

[RESULTS] A total of 748 patients were included in the study, representing five tumor types. Prevalence of dMMR varied across tumor types, with an overall prevalence of 9.4%. Patients with endometrial tumors had the highest proportion of patients with dMMR at 49/164 (29.9%). Patients with cervical tumors had the lowest prevalence of dMMR with 6/221 (2.7%) patients. The prevalence of dMMR was similar across most demographic characteristics. In the dMMR population, co-occurring MLH1 and PMS2 protein loss across all tumor types was observed most commonly, in 48/70 (68.6%) patients.

[CONCLUSIONS] These data highlight the importance of dMMR testing in patients with advanced solid tumors in China to optimize biomarker testing and treatment decisions.