Familial adenomatous polyposis
Familial adenomatous polyposis is a rare, inherited condition that causes extra tissue (polyps) to form in your large intestine (colon) and rectum. Polyps can also occur in the upper gastrointestinal tract, especially the upper part of your small intestine (duodenum). If untreated, the polyps in the colon and rectum are likely to become cancerous in your 40s. Some people have a milder form of the condition called attenuated familial adenomatous polyposis (AFAP) which is generally characterized by fewer colon polyps (an average of 30) and a delay in the development of colon cancer by 10-15 years.
Most people with familial adenomatous polyposis eventually need surgery to remove the large intestine to prevent cancer. The polyps in the duodenum also can develop cancer, but they can usually be managed by careful monitoring and removing polyps regularly.
Familial adenomatous polyposis is caused by a defect in the adenomatous polyposis coli (APC) gene. Most people inherit the genetic abnormality from a parent. But in about 25 percent of cases, the genetic mutation occurs spontaneously.
The abnormal gene causes hundreds or even thousands of polyps to grow in your colon and rectum, usually starting by your mid-teens. The polyps are nearly 100 percent certain to develop into colon cancer or rectal cancer by the time you're in your 40s.
Familial adenomatous polyposis can cause other complications:
- Duodenal polyps. These polyps grow in the upper part of your small intestine and may become cancerous. But with careful monitoring, duodenal polyps can often be detected and removed before cancer develops.
- Periampullary polyps. These polyps occur where the bile and pancreas ducts enter the duodenum (ampulla). Periampullary polyps might become cancerous but can often be detected and removed before cancer develops.
- Desmoids. These noncancerous masses can arise anywhere in the body but often develop in the stomach area (abdomen). Desmoids can cause serious problems if they grow into nerves or blood vessels or exert pressure on other organs in your body.
- Other cancers. Rarely, FAP can cause cancer to develop in your thyroid gland, central nervous system, adrenal glands, liver or other organs.
- Noncancerous skin tumors.
- Noncancerous bone tumors.
- Pigment changes in the retina of your eye.
- Dental abnormalities.
The signs and symptoms of familial adenomatous polyposis (FAP) vary both within families and between families. Classic FAP is characterized primarily by hundreds to thousands of noncancerous (benign) polyps (growths) in the colon that begin to appear at an average age of 16 years. Unless the colon is removed, these polyps will become malignant (cancerous), leading to early-onset colorectal cancer at an average age of 39 years.
Other features of FAP may include:
- Fundic gland or adenomatous polyps of the stomach
- Adenomatous polyps of the small intestines
- Osteomas (benign bone tumors)
- Dental abnormalities
- Congenital hypertrophy of the retinal pigment epithelium (a flat, pigmented spot within the outer layer of the retina)
- Benign skin abnormalities
- Adrenal masses
- Desmoid tumors
- Other types of cancer (small bowel, stomach, pancreas, thyroid, central nervous system, liver, bile ducts, and/or adrenal gland)
- Benign and malignant tumors of the duodenum (a section of the small intestine), stomach, bones, skin, and other tissues
FAP is caused by changes (mutations) in the APC gene and is inherited in an autosomal dominant manner. People with FAP usually undergo regular screening until they develop 20 to 30 polyps and then a colectomy (removal of colon) is generally recommended.
These mutations affect the ability of the cell to maintain normal growth and function. Cell overgrowth resulting from mutations in the APC gene leads to the colon polyps seen in familial adenomatous polyposis. Although most people with mutations in the APC gene will develop colorectal cancer, the number of polyps and the time frame in which they become malignant depend on the location of the mutation in the gene.
Mutations in the MUTYH gene cause autosomal recessive familial adenomatous polyposis (also called MYH-associated polyposis). Mutations in this gene prevent cells from correcting mistakes that are made when DNA is copied (DNA replication) in preparation for cell division. As these mistakes build up in a person's DNA, the likelihood of cell overgrowth increases, leading to colon polyps and the possibility of colon cancer.
Familial adenomatous polyposis can have different inheritance patterns. When familial adenomatous polyposis results from mutations in the APC gene, it is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder. In most cases, an affected person has one parent with the condition.
When familial adenomatous polyposis results from mutations in the MUTYH gene, it is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. Most often, the parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but do not show signs and symptoms of the condition.
Genetic testing is available for the gene known to cause familial adenomatous polyposis. Prenatal testing and genetic testing for at-risk relatives are possible if the disease-causing mutation in the family is known. Because colon screening for those at risk for classic FAP begins as early as age ten years, genetic testing is generally offered to children by this age. Testing may be offered earlier if the child is showing signs or symptoms of FAP.
The timing of this operation depends on several factors. Since FAP usually appears in young people, certain lifestyle issues must be considered. It may take a while to accept the idea of having your colon removed. Also, there may not be a large number of polyps present at the time of diagnosis, and a decision may be made to closely monitor the subsequent growth. Colonoscopy is the method of choice for monitoring the growth and numbers of the polyps in FAP patients. Biopsy or removal of the largest polyps or the most suspicious-looking ones may also be done at colonoscopy. By definition, all adenomatous polyps have elements of dysplasia (abnormal cell growth). Dysplasia is a precursor to cancer and is graded from mild to severe. It is almost certain that a patient with FAP will eventually develop severe dysplasia in a polyp -- indicating the transformation to cancer is very near.
Prior to reaching the advanced stages of colorectal cancer, the polyps are confined to the inner wall and thickness of the intestinal tract and do not metastatise or 'spread'. So provided FAP is detected and controlled either at the pre-cancerous stage or when any cancerous polyps are still internal to the intestinal tract, surgery has a very high success rate of preventing or removing cancer, without recurrence, since the locations giving rise to cancer are physically removed in toto by the surgery.
Following surgery, if a partial colectomy has been performed, colonoscopic surveillance of the remaining colon is necessary as the individual still has a risk of developing colon cancer. However, if this happened, it would be a fresh incident from polyps developing anew in the unremoved part of the colon subsequent to surgery, rather than a return or metastasis of any cancer removed by the original surgery.
Treatment for FAP depends on the genotype. Most individuals with the APC mutation will develop colon cancer by the age of 40, although the less-common attenuated version typically manifests later in life (40–70). Accordingly, in many cases, prophylactic surgery may be recommended before the age of 25, or upon detection if actively monitored. There are several surgical options that involve the removal of either the colon or both the colon and rectum.
- Rectum involved: the rectum and part or all of the colon are removed. The patient may require an ileostomy (permanent stoma where stool goes into a bag on the abdomen) or have an ileo-anal pouch reconstruction. The decision to remove the rectum depends on the number of polyps in the rectum as well as the family history. If the rectum has few polyps, the colon is partly or fully removed and the small bowel (ileum) can be directly connected to the rectum instead (ileorectal anastomosis).
- Rectum not involved: the portion of the colon manifesting polyps can be removed and the ends 'rejoined' (partial colectomy), a surgery that has a substantial healing time, but leaves quality of life largely intact.
Prophylactic colectomy is indicated if more than a hundred polyps are present, if there are severely dysplastic polyps, or if multiple polyps larger than 1 cm are present.
Treatment for the two milder forms of FAP may be substantially different from the more usual variant, as the number of polyps are far fewer, allowing more options.
Various medications are being investigated for slowing malignant degeneration of polyps, most prominently the non-steroidal anti-inflammatory drugs (NSAIDs). NSAIDS have been shown to significantly decrease the number of polyps but do not usually alter management since there are still too many polyps to be followed and treated endoscopically.
Recently, a drug was approved for the medical treatment of patients with FAP. This drug, celecoxib (Celebrex) is an anti-inflammatory drug that inhibits an enzyme known as cyclooxygenase 2 (COX-2). Colon polyps produce large amounts of COX-2. Studies have shown that celecoxib and other COX-2 inhibitors can slow the growth of polyps and even reduce the number of polyps in patients with FAP. However, it must be stressed that COX-2 inhibitors are not a cure for FAP, or even a substitute for eventual surgical removal of the colon in patents with FAP.
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