31st December 2024

Hereditary non-polyposis colorectal carcinoma

Hereditary non-polyposis colorectal carcinoma (HNPCC, 5%), also called Lynch syndrome, is an autosomal dominant condition due to mutation in mismatch repair genes – MSH2 in 60% of cases and MLH1 in 30%. The lifetime risk of colorectal cancer is around 80%. There is also increased risk of other ‘Lynch cancers’: endometrial, ovarian, urinary tract, stomach, small bowel and hepatobiliary.

Diagnosis is suspected if there are 3 or more affected relatives (one of whom must be 1st degree) from 2 successive generations, of whom one was affected when under 50 years old. Asymptomatic relatives of patients with Lynch syndrome may be offered genetic testing.

Colonic surveillance at least every other year is advised from age 25 to 75, with the aim being early detection of Lynch syndrome-associated cancers and surgery where necessary.