Interpretation of genetic testing for lynch syndrome in patients with putative familial colorectal cancer.

Colorectal cancer (CRC) risk assessment involves the evaluation of an individual's personal and family history for characteristics of an inherited susceptibility to develop CRC. Lynch syndrome (LS), or hereditary nonpolyposis colorectal cancer, is the most common cause of hereditary CRC, underlying 2% to 3% of patients with newly diagnosed (incident) CRC. Risk assessment for LS is complex, and the interpretation of the many available tests can be challenging even for the genetics specialist. A move toward universal (reflex) LS screening for mismatch repair in all patients with incident CRC supports the importance of improving the awareness and understanding of LS testing, teaching rational testing approaches, and honing interpretive skills among cancer care providers. This article reviews important clinical features of LS genetic evaluation using 3 pedigree-based case examples from the Fox Chase Cancer Center Gastrointestinal Risk Assessment Clinic.