The two main inherited colorectal cancer syndromes are familial adenomatous polyposis (FAP) and Lynch syndrome (hereditary nonpolyposis colorectal cancer [HNPCC]), which account for less than 1 % and 3 % of colorectal cancers, respectively. FAP is characterized by the occurrence of multiple colorectal adenomas that often start to develop during the teenage years. A germ-line mutation in the APC gene located on chromosome 5 is found in about 85 % of patients with this phenotype. Without prophylactic surgery, nearly all will develop colorectal cancer. Surgery, including restorative proctocolectomy or total colectomy with ileorectal anastomosis, has greatly reduced the death rate from colorectal cancer, and now prognosis is dependent on desmoid tumors and duodenal polyposis.
HNPCC syndrome is more complex than FAP because more genes are involved, penetrance is less complete, and expression varies more. The recommendation is to try to determine the microsatellite instability (MSI) phenotype to test patients showing an MSI. Screening guidelines are well defined. Surgical management of HNPCC using segmental versus total colectomy is still debated.
A third syndrome, the MYH-associated polyposis syndrome, related to germ-line biallelic mutation of the human MUTYH gene, is an autosomal-recessive colon cancer syndrome. Other syndromes such as Peutz Jeghers syndrome, juvenile polyposis, and hyperplastic polyposis are seen less frequently.