A condition in which pathogenic variants of the MLH1, MSH2, MSH6, and PMS2 genes or the deletion of the EPCAM gene located just upstream of the MSH2 gene [1–3] are congenitally detected is called Lynch syndrome, and tumors developing in patients with Lynch syndrome are called Lynch-associated tumors (refer to “Lynch syndrome” [4, 5]). Here, MSH2 is linked to Lynch syndrome.