Pattern of Deficient Mismatch Repair (dMMR)/ High Microsatellite Instability (MSI-H) Testing in India: A...

Introduction Deficient mismatch repair (dMMR) and high microsatellite instability (MSI-H) constitute a unique phenotype within solid tumors, particularly colorectal, endometrial, and gastric cancer. They offer prognostic significance and serve as a predictor for responses to immunotherapy. The current study aimed to understand the practices, attitudes, and barriers associated with dMMR/MSI-H testing among medical oncologists in India. Methods This study was a cross-sectional survey utilizing a questionnaire, where Indian oncologists were selected through a convenience sampling method. A structured questionnaire consisting of 20 questions was developed, capturing comprehensive information on practices, preferences, and challenges faced by doctors during dMMR/MSI-H testing. A descriptive analysis was performed on the compiled data. Results A significant proportion of doctors (n=35, 62.5%) indicated a general preference for incorporating dMMR/MSI-H testing into their clinical practice. More than half of them believed that positive test results would be observed in 5-15% of patients with metastatic and non-metastatic colon and endometrial tumors. Immunohistochemistry (IHC) emerged as the preferred testing method, with 84% of oncologists usually conducting it as the first test. The issues of affordability and the subsequent awareness among oncologists emerged as a major barrier to the adoption of polymerase chain reaction (PCR) and next-generation sequencing (NGS) techniques for assessing MSI status. The vast majority (89%) agreed with the importance of detecting MSI status when assessing suitability for treatment with PD-1/PD-L1 inhibitors in solid tumor patients.  Conclusions A deeper understanding of the importance of dMMR/MSI-H status in the clinical characteristics and prognosis of solid tumors, especially colorectal, gastroesophageal, and endometrial cancers, may lead to increased adoption of dMMR/MSI-H testing and guide the development of more effective therapies.