Approximately 2% of all colon cancer is thought to be caused by an adenomatous polyposis condition. They can be categorized into three conditions:
- Familial adenomatous polyposis (FAP)
- Attentuated familial adenomatous polyposis (aFAP)
- MYH-associated polyposis (MAP)
Familial adenomatous polyposis (FAP) is caused by a mutation in the adenomotous polyposis coli (APC) gene resulting in “gastrointestinal polyposis,” which is the presence of many growths (polyps) throughout the gastrointestinal tract. Hundreds to thousands of polyps can grow in the large intestine (colon and rectum) and one of these polyps will, eventually, develop into an invasive colon cancer unless surgery is performed to remove the colon and rectum before this happens. A person will develop this disease if they inherit a single mutated gene from either parent. If a person carries this mutation, there is a 50% chance of passing the disease onto his/her children. This mutation can also occur spontaneously in an individual, when neither parent carried the mutation (this occurs in about 20% of FAP patients). Patients usually develop polyps in their early 20s and, if untreated, cancer usually develops by 39 years of age.
Attenuated familial adenomatous polyposis (aFAP) is a milder form of FAP, with colonic adenomas numbering anywhere from 1 to 100 in number. The development of polyps and cancer may also delayed, generally being detected 10 to 15 years later than in the classic form of FAP. However, this may be more a result of the lack of awareness and obvious family history associated with the attenuated form of disease rather than a true delay in polyp development and close surveillance remains of paramount importance.
MYH-associated polyposis (MAP) is a third type of polyposis syndrome. This is caused by mutations in a completely different gene, the mutY homolog or MYH gene. Unlike FAP and aFAP, individuals must have inherited two mutated genes (one from each parent) in order to develop the syndrome. The parents themselves most likely had one normal and one mutated gene and, therefore, were unaffected by the disease. Therefore, patients often have no family history of colon cancer or polyps but they, and their siblings, may be affected and develop 100 to 1,000 polyps and, eventually, colon cancer.
What Are the Signs and Symptoms of Polyposis Syndromes?
- Most importantly, people often have a history of colorectal cancer or multiple polyps developing at a young age in members of their immediate family.
- Nonspecific symptoms, such as rectal bleeding, diarrhea and abdominal pain in young people may suggest the presence of one of these syndromes.
- Most people don’t have symptoms until they develop colon cancer at an early age (usually before age 50).
How Are Polyposis Syndromes Diagnosed?
The key to diagnosis of a polyposis syndrome is a high level of suspicion and obtaining a comprehensive family history which is suggestive of an Inherited Colorectal Cancer Syndrome. The next step involves screening, which should begin in childhood.
- Frequent colonoscopic exams are essential to rule out malignant changes in polyps.
- Genetic testing should also be performed.
- Upper endoscopy is also needed to check for polyps in the stomach and duodenum.
- An eye examination in a child of a parent with known FAP can also help with early diagnosis.
How Are Polyposis Syndromes Treated?
People with a polyposis syndrome often develop hundreds to thousands of polyps, making it prohibitively dangerous and time-consuming to remove them individually. In addition, the risk of developing colon cancer at some time is inevitable. Surgery to remove the whole colon and rectum (Proctocolectomy) is the only effective treatment and has been shown to greatly improve life expectancy. Variations on this surgery, such as Ileal Pouch Anal Anastomosis and Ileorectal Anastomosis Surgery can be done in adulthood; however, because of the high risk of colon cancer, we may encourage earlier surgical intervention based on the number and distribution of polyps present. Continued surveillance is needed after surgery to be sure polyps are not developing in other areas of the gastrointestinal tract or if any rectal tissue remains after surgery. Certain medicines (sulindac, celecoxib) may make polyps shrink or prevent new growths, but should be used only with regular check-ups and screening. Upper endoscopy to find polyps, genetic testing, and screening of family members are needed.