Microsatellite instability (MSI) in tumors is a known predictor of response to certain therapies in gynecological cancer. In this video, Alexandra Leary, MD, PhD, of the Gustave Roussy Institute of Oncology, Paris, France, discusses utilizing MSI as a clinical biomarker in gynecological tumors to guide treatment. Speaking from the UK Oncology Forum (OF) 2018, in Liverpool, UK, she explores trial data suggesting that MSI is an indicator for positive immunotherapy responses, which should be implemented for relapsed endometrial cancer patients within Europe. Moreover, Dr Leary highlights the clinical benefits of the MSI test in terms of both ease and cost.