By Dr. Phil Hassard, Gastroenterologist
About 75% of cases of colorectal cancer (CRC) are sporadic, 20% of cases occur in people with a family history; while about 5% of cases occur in patients with inflammatory bowel disease or genetic mutations. Average risk individuals have multiple screening options. In high-risk patients, however, earlier and more frequent screening (generally with colonoscopy) is required to reduce the risk of advanced neoplasia.
Taking a history of colon cancer or advanced adenomas in first degree relatives is important to risk stratify patients. A family history of advanced adenoma increases lifetime relative risk 2 fold, and a first-degree relative with CRC increases lifetime risk about 2.5 fold. Multiple first-degree relatives affected increases risk about 4 fold. The effect of family history is more pronounced when the affected relative is under age 60. Patients with a family history of CRC should be considered for colonoscopy starting at age 50 or 10 years earlier than the youngest first degree relative affected.
Inflammatory bowel diseases (Crohn’s disease and ulcerative colitis) are conditions that predispose to CRC. Although the magnitude of this risk is controversial, it relates to duration, extent and severity of disease. These patients are usually followed by a specialist and generally require regular colonoscopies after 8-10 years of disease. Earlier screening is needed in patients with primary sclerosing cholangitis. Screening technique has traditionally consisted of biopsies, but more recent evidence suggests that dye-spraying may be more effective in finding dysplasia in IBD.
Certain rare genetic syndromes confer a very high risk of CRC, including hereditary non-polyposis colon cancer (HNPCC), familial adenomatous polyposis (FAP), Peutz-Jeghers syndrome and familial juvenile polyposis. If there is a very strong history of CRC in multiple relatives at early ages, early screening and genetic testing are recommended. Other groups to consider for earlier screening include African-Canadians, patients with acromegaly, and renal transplant recipients. In conclusion, high-risk patients need to be identified early in order to commence appropriate screening. Carefully reviewing the family history and being aware of predisposing conditions is essential to minimizing the risk of CRC in these patients.