Lynch Syndrome and MYH-Associated Polyposis: Review and Testing Strategy

Individuals with Lynch syndrome have an increased risk for colorectal cancer, endometrial cancer, and other associated cancers such as gastric cancer, ovarian cancer, urothelial cancers, hepatobiliary tract cancer, brain cancer, cancer of the small intestine, pancreatic cancer, and particular skin cancers. Lynch syndrome caused by defects in DNA mismatch repair genes, and diagnostic testing for Lynch syndrome begins with microsatellite instability and immunohistochemical analysis on the tumor specimen followed by germline genetic testing and possibly further studies on the tumor. MYH-associated polyposis syndrome is a recently characterized, autosomal recessive, polyposis syndrome caused by biallelic mutations in the MYH gene. Individuals carrying 2 copies of the mutation have a significantly increased risk of polyposis, colorectal cancer, upper gastrointestinal polyps and additional features commonly seen in familial adenomatous polyposis syndrome. Genetic testing for MYH mutation is complicated by the phenotypic overlap of MYH-associated polyposis with other colorectal cancer syndromes. This study serves to clarify the best testing approach.