19th July 2023

Hereditary Non-Polyposis Colorectal Cancer (HNPCC)

HNPCC, aka Lynch syndrome, is an autosomal dominant inherited condition that increases the risk of various malignancies – most commonly CRC(60-80%). It is caused by a defect in a mismatch repair gene, usually MSH2 or MLH1 (90%), causing microsatellite instability. It is the most common hereditary CRC syndrome, responsible for 1-3% of all CRCs. Other malignancies that are commonly associated with HNPCC include endometrial, ovarian, small bowel and liver cancer. The Amsterdam clinical criteria aids diagnosis alongside molecular genetic testing for germline mutations. Patients with HNPCC undergo 2 yearly colonoscopy screening, with the onset of screening determined by the causative gene mutation. All patients should be offered aspirin, which reduces the risk of developing CRC. If a high risk gene mutation is identified, subtotal bowel resection should be considered.