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Colorectal cancer (CRC) incidence is declining in people aged ≥50 years in the U.S. and rising in those aged <50 years. It's generally considered that most of the increased risk in younger people is not inherited risk. Current protocols call for genetic testing in patients with polyposis phenotypes, strong family histories, and those whose tumors demonstrate microsatellite instability or fail to stain for mismatch repair gene proteins by immunohistochemistry.
In a retrospective study of pathogenic germline mutation risk in 430 patients with CRC diagnosed at age <50 years, 6% had polyposis phenotypes and 26% had a family history of CRC. Clinically driven genetic testing identified germline mutations in 79 patients (18%), and additional sequen…