[Providing Opportunities for Close Examination of Lynch Syndrome after Microsatellite Instability Testing in a...

Microsatellite instability(MSI)testing is performed in cancer patients to determine the indication for chemotherapy with immune checkpoint inhibitors. We report on our scheme to ensure that Lynch syndrome patients are offered the opportunity for genetic counseling and genetic testing. Two hundred and eight cancer patients(107 males and 101 females, 20- 87 years, mean 63.3 years)underwent MSI testing at our hospital between February 2019 and November 2021. From February 2019 to December 2020, the MSI testing was performed with a consent document that included a commentary on Lynch syndrome, and the results were explained only by the attending cancer doctors. Eleven(8.6%)of the 136 cases had MSI-high, but none of them led to a visit to the genetic medicine department. The Genome Center in our hospital, which was operational from April 2020, undertook information sharing by multiple professions and established a system to provide appropriate support to cancer doctors. Consecutively, 72 MSI tests were performed between January and November 2021, and 2 patients(2.8%)with MSI-high(1 with endometrial cancer and 1 with colorectal cancer)were referred to the Department of Clinical Genetics for genetic counseling. Through genetic testing, both were diagnosed with Lynch syndrome, and information on future surveillance and health care for blood relatives was provided.