Dr. Cameron Schauer
Polyposis syndromes are a group of conditions in which multiple polyps occur, conferring an increased risk of colorectal cancer (CRC) and potentially cancers outside the colon as well. They are often inherited, and a careful assessment of family history is paramount.
Familial adenomatous polyposis is the best characterised of the polyposis syndromes, occurring in two to three out of every 100,000 persons. It has autosomal dominant inheritance with a mutation of the APC tumour suppressor gene. However, 30 per cent of cases do not have a family history, suggesting de novo mutation. It is characterised by hundreds to thousands of adenomas that start to appear in the second decade of life. There is close to a 100 per cent chance of developing CRC (87 per cent chance at age 45), and prophylactic colonic resection is advised. Additional screening for upper gastrointestinal malignancy is also performed.
Sessile serrated polyposis syndrome is characterised by numerous sessile serrated polyps, with an estimated incidence of one in 3000 persons. Its aetiology is not well understood, and genetic testing is not useful, although 50 per cent of individuals have a family history of CRC. A diagnosis is made when an individual is found to have over 20 serrated polyps throughout the colon, or when there are at least five such polyps but two are more than 1cm in size. As many as 30–50 per cent of patients may present with CRC already. Once diagnosed, multiple colonoscopies with polyp removal are often required to reduce the burden of polyps, which are then spaced every one to two years to remove further growth. First-degree relatives have a fivefold increased risk of CRC and are advised to have a colonoscopy every five years.
Lynch syndrome
Previously known as hereditary non-polyposis colorectal cancer, this syndrome confers up to a 50 per cent risk of developing CRC by age 70. It is estimated to account for 3–5 per cent of CRC cases, with nearly half diagnosed before age 50. It has autosomal dominant inheritance of one of four identified mismatch repair genes. Screening for polyps with colonoscopy is suggested to start from age 25, and thereafter on a one to two-yearly basis. Additional screening is recommended for extracolonic malignancy, including for development of small bowel, uterine, urinary tract and ovarian cancers.
Summary:
The majority of CRC arises from polyps. Features and characteristics of the polyps confer risk of CRC development. A strong family history or multiple (>10) polyps in a patient should trigger consideration of a polyposis syndrome.