Adenomatous Polyposis Coli (APC) is a rare, inherited condition characterized by numerous polyps, predominantly within the colon and rectum. This genetic disorder significantly increases the likelihood of developing colorectal cancer.
The Genetic Basis
Adenomatous Polyposis Coli is caused by a mutation in the APC gene. This gene normally functions as a tumor suppressor, regulating cell growth and division. When mutated, its ability to control cell proliferation is impaired, leading to unchecked cell growth and polyp formation.
This condition typically follows an autosomal dominant inheritance pattern, meaning an individual needs only one copy of the mutated APC gene from either parent to develop it. If one parent has APC, each child has a 50% chance of inheriting the mutated gene. While most cases are inherited, approximately 20% to 30% of individuals diagnosed with APC may have a new mutation not inherited from either parent.
Development of Polyps and Cancer Risk
An APC gene mutation leads to the formation of adenomatous polyps, benign growths in the colon and rectum lining. These polyps are precancerous and can become malignant over time. Individuals with classic APC typically develop hundreds to thousands of these polyps, often beginning in their teenage years.
Without intervention, there is an almost 100% lifetime risk of developing colorectal cancer for individuals with classic APC, often by age 39. The sheer number of polyps makes individual removal impractical, necessitating comprehensive management. While colorectal cancer is the primary concern, polyps can also develop in other gastrointestinal areas, including the stomach and duodenum, and carry an increased risk of other cancers such as those of the small intestine, thyroid, pancreas, and brain.
Detection and Surveillance
Identifying Adenomatous Polyposis Coli often involves genetic testing for the APC gene mutation, especially for family members. Genetic testing confirms the mutation, even before symptoms, and helps distinguish between classic and attenuated forms of APC. For those at risk or with a known family history, genetic testing is often recommended for children aged 10 to 15.
The primary method for diagnosing and monitoring APC is a colonoscopy. This procedure allows for a visual inspection of the colon and rectum to detect and assess polyps. For individuals with APC, colonoscopies typically begin between 10 and 12 years of age and are performed annually or every one to two years, depending on the specific guidelines and polyp burden. Upper endoscopies are also recommended, usually starting between 20 and 25 years of age, to screen for polyps in the stomach and duodenum.
Treatment and Long-Term Care
The primary treatment for Adenomatous Polyposis Coli is prophylactic surgery to remove the colon and rectum, significantly reducing cancer risk. This surgery is typically performed in early adulthood, before cancer develops, due to the inevitable progression of polyps to malignancy. Several surgical procedures exist, including total colectomy with ileorectal anastomosis, total proctocolectomy with ileostomy, or restorative proctocolectomy with ileal pouch-anal anastomosis (J-pouch surgery). The specific option chosen depends on the extent of polyposis and patient preference for bowel function.
Even after surgery, ongoing surveillance remains crucial. This includes regular endoscopic examinations of any remaining rectal tissue or the ileal pouch to detect new polyp formation. Individuals with APC also require continued monitoring for extracolonic manifestations, which are growths or cancers that can occur outside the colon, such as desmoid tumors, and cancers of the small bowel, thyroid, or stomach. A multidisciplinary care team, involving gastroenterologists, surgeons, and genetic counselors, is essential to provide comprehensive and individualized long-term management for those with APC.