Familial adenomatous polyposis

BACKGROUND

Polyps may be seen in a patient's upper intestine as well. About one in 30,000 people is affected with FAP.

Polyps usually begin to grow in patients at about age 10 to 12. Initially, these polyps do not cause symptoms in most patients. However, they greatly increase the risk of colon cancer, in which cells in the colon divide uncontrollably and develop into tumors. Almost all patients with FAP develop colon cancer by age 40.

FAP is known to be caused by mutations in a gene called adenomatous polyposis coli or APC (APC). This gene contains the genetic code for making the APC protein, which regulates growth in normally functioning cells. Mutations in the APC gene can result in an abnormal APC protein that cannot properly control cell growth. This leads to the formation of polyps in patients with FAP.

If the polyps are removed before cancer develops, patients may greatly reduce their risk of developing cancer. If colon cancer does develop, it can be life-threatening. However, it can be treated in a number of ways, including surgery, radiation therapy, and chemotherapy.

RISK FACTORS

Because familial adenomatous polyposis (FAP) is inherited, a family history of the disease is the main risk factor.

About 6% of people with Ashkenazi Jewish Heritage have a mutant variant of the APC gene (an amino acid substitution at one position in the gene) that may increase the risk of developing colon cancer by 10-20%.

CAUSES

General: Familial adenomatous polyposis coli (FAP) is known to be caused by mutations in a gene called adenomatous polyposis coli or APC. This gene contains the genetic code for making the APC protein, which normally functions in cells to regulate cell growth. Mutations in the APC gene can result in an abnormal APC protein that cannot properly control cell growth. This leads to the formation of polyps in patients with FAP.

More than 700 different mutations in the APC gene may lead to FAP. The most common disease-causing mutations in the APC gene result in the production of a shortened version of the APC protein that is unable to function normally. Some mutations in the APC gene lead to more severe forms of FAP (more polyps and faster onset) than other mutations.

Inheritance: Most cases of familial adenomatous polyposis (FAP) are inherited, meaning that a defective gene was transmitted from a parent to the child. Patients with FAP may have a mutation, or genetic error, in a gene called adenomatous polyposis coli or APC. Individuals receive two copies of most genes (one from the mother and one from the father). In patients with FAP, at least one copy of the APC gene appears to be defective.

If an individual has a parent with one mutant APC gene, that individual has a 50% chance of inheriting a mutant APC gene and developing the disease. Because only one defective gene is needed for FAP to develop, the disease is considered to follow an autosomal dominant inheritance pattern.

Some cases of FAP follow an autosomal recessive inheritance pattern, meaning two abnormal copies of a gene are needed for the condition to develop. The recessive form of FAP (also called MYH-associated polyposis) is caused by mutations in the MUTYH gene. This gene makes a protein called MYH glycosylase, which is an enzyme that repairs mistakes in DNA.

Random occurrence: About a third of cases of FAP are not inherited, but instead result from a spontaneously arising mutation in the APC gene in the egg, sperm, or in early embryonic development.

Other: FAP may also be caused by mutations in the MUTYH gene. This gene makes a protein called MYH glycosylase, which is an enzyme that repairs mistakes in DNA. Mistakes may occur in DNA during cell division and these mistakes may cause other genes to undergo mutations and to function incorrectly. In individuals with MUTYH mutations, mistakes may accumulate in the DNA because they are not properly repaired. Over time, these mutations may cause cells to grow abnormally, which could eventually lead to cancer.

About two-thirds of patients with Turcot syndrome have mutations in the APC gene. Turcot syndrome is a condition that is related to FAP. Patients with Turcot syndrome develop colorectal cancer along with brain cancer.

SIGNS AND SYMPTOMS

Patients with familial adenomatous polyposis coli (FAP) experience the growth of hundreds to thousands of polyps (an abnormal mushroom-shaped growth of tissue) in the lower intestine (including the colon and rectum). Growth of polyps may be seen in a patient's upper intestine as well. The number of polyps usually increases with age and they typically grow from 1-2 to 4-5 millimeters in size.

Most patients do not experience any symptoms early on as a result of the polyps. As the polyps grow in size, they may bleed and cause some patients to experience blood in the stool. Other gastrointestinal problems may occur, including diarrhea and abdominal pain. The polyps have a high likelihood of becoming cancerous.

In some patients, polyps may also grow in the upper intestine (duodenum) or even in the stomach. These polyps have a much lower risk of becoming cancerous than polyps in the colon or rectum.

A large number of patients with FAP develop small "freckles" at the back of the retina (also called congenital hypertrophy of the retinal pigment epithelium). These pigmented lesions are considered one of the first signs of the disease and can sometimes be observed in infants. However, these freckles are benign (harmless) and do not cause any symptoms. Some patients with FAP may also develop lumps or bumps on the bones, which may affect any part of the skeleton. Cysts, or fluid filled sacs, may also develop on the skin.

DIAGNOSIS

Familial adenomatous polyposis (FAP) is usually diagnosed by checking for the presence of polyps in a patient's colon. There are several methods that can be used to screen for polyps. Patients who have a family history of FAP are encouraged to undergo screening early on (in their teens) so that polyps can be detected before cancer has a chance to develop.

Colonoscopy: Doctors may perform a colonoscopy to check for polyps in the colon. In a colonoscopy, a flexible tube with a light attached (called an endoscope) is inserted through a patient's anus. The endoscope can transmit images of the patient's colon to the doctor so that any polyps can be observed.

Barium enema: To visualize the entire large intestine, a liquid dye called barium may be used to fill and coat a patient's intestine. Then, a doctor uses X-rays to take pictures of the patient's intestine. The barium will cause any polyps along the lining of the intestine to appear as dark areas on the X-ray image, allowing the polyps to be observed.

Computed tomography: An imaging technique called a computed tomography (CT) scan may be used to observe polyps in a patient's colon. A CT scan is a noninvasive imaging technique that uses a series of X-rays to create detailed three-dimensional images of the inside of a patient's body. Polyps can then be detected in these images.

Genetic testing: Mutations in the APC gene or MUTYH gene are known to cause FAP. Genetic tests can be used to check for these mutations and diagnose FAP. These tests may confirm a diagnosis if there is a family history of FAP or if symptoms of FAP are present.

COMPLICATIONS

Colon cancer: The most common complication in patients with familial adenomatous polyposis (FAP) is colon cancer. About one percent of all cases of colon cancer are due to FAP, and all patients with FAP develop colon cancer by the time they are 40. Colon cancer is a disease in which the growth of cells in the colon has become deregulated, such that they divide uncontrollably and develop tumors. Colon cancer is a potentially life-threatening condition, and further complications may result when tumor cells metastasize (spread) to other tissues. Prognosis is worst in cases where the tumor has metastasized to other areas of the body such as the liver.

Desmoid tumors: Some patients with FAP develop tumors that are not cancerous, called desmoid tumors. These fibrous tumors are similar to scar tissue, and they often develop in the abdomen. Even though they are not cancerous, they may cause pain if they grow large enough to block a blood vessel or the bowel. Desmoid tumors may be surgically removed but usually grow back after removal.

TREATMENT

If polyps are found at an early stage before cancer has a chance to develop, they can be surgically removed. Patients with familial adenomatous polyposis (FAP) who have polyps removed early in the disease have a very high chance of not developing cancer (near 100%).

There are often too many polyps present to remove each one individually. Depending on the extent of the disease, a patient will need to have the entire colon removed (a colectomy) or the colon, rectum, and in some cases the anus removed (a proctocolectomy).

In a colectomy, the colon is removed, and the small intestine is surgically connected directly to the anus. In a proctocolectomy in which the colon and rectum are removed, a small pouch is inserted to connect the small intestine to the anus and allow the passage of waste. In a proctocolectomy in which the colon, rectum, and anus have been removed, a portion of the intestine may be brought out through a hole in the abdominal wall, so waste can be directly delivered to an external bag.

Patients who undergo surgery need to have frequent checkups (every three to twelve months) to ensure that polyps do not begin to form in other parts of the digestive tract, such as the stomach, upper third of the small intestine (duodenum), or rectum (if it was not initially removed). If new polyps are observed, patients may need to undergo additional surgeries.

In patients who do not have polyps removed promptly and as a result develop cancer, a number of treatments are available to help to control the tumor growth. Tumors may be removed surgically or cancer cells may be killed with radiation or with drugs (such as irinotecan, oxaliplatin, and 5-fluorouracil). Patients who develop cancer should consult with a physician to determine the best therapy. If treated at an early stage, patients who develop colon cancer have a good chance of surviving.

INTEGRATIVE THERAPIES

Note: Currently, there is a lack of scientific data on the use of integrative therapies for the treatment or prevention of familial adenomatous polyposis (FAP). The therapies listed below have been studied for related conditions, such as colon cancer, and should be used only under the supervision of a qualified healthcare provider, and not as a replacement for other proven therapies or preventive measures.

Good scientific evidence:

Lactobacillus casei: There is recent evidence that supplementation with Lactobacillus casei may help reduce the recurrence of colorectal tumors in patients who have previously undergone surgery for colon cancer. Probiotics are generally regarded as safe for human consumption. Long-term consumption of probiotics is considered safe and well-tolerated.

Unclear or conflicting scientific evidence:

Omega-3 fatty acids: Omega-3 fatty acids are commonly taken by cancer patients. Although preliminary studies report that growth of colon cancer cells may be reduced by taking fish oil, effects on survival or remission have not been measured adequately. Omega-3 fatty acids may increase the risk of bleeding, although there is little evidence of significant bleeding risk at lower doses. Very large intakes of fish oil/omega-3 fatty acids may increase the risk of hemorrhagic (bleeding) stroke. High doses have also been associated with nosebleed and blood in the urine. Fish oils appear to decrease platelet aggregation and prolong bleeding time, increase fibrinolysis (breaking down of blood clots), and may reduce levels of von Willebrand factor.

Psyllium: According to early research, diets that include psyllium may reduce the risk for colon cancer. More studies are needed to determine whether psyllium can help prevent colon cancer. Serious allergic reactions including anaphylaxis, difficulty breathing/wheezing, skin rash, and hives have been reported after the ingestion of psyllium products. Less severe hypersensitivity reactions have also been noted. Cross-sensitivity may occur in people with allergy to English plantain pollen (Plantago lanceolata), grass pollen, or melon.

Soy: Soy (Glycine max) contains compounds that have shown efficacy against tumors. Genistein, an isoflavone found in soy, has been found in laboratory and animal studies to possess anti-cancer effects, such as blocking new blood vessel growth (anti-angiogenesis), acting as a tyrosine kinase inhibitor (a mechanism of many new cancer treatments), or causing cancer cell death (apoptosis). In contrast, genistein has also been reported to increase the growth of pancreatic tumor cells in laboratory research. There is currently insufficient scientific evidence to determine if dietary intake of soy affects the risk of developing colon cancer. Study results are mixed and more research is needed before a recommendation can be made.

Vitamin E: Reliable scientific evidence indicating that vitamin E is an effective treatment for any specific type of cancer is currently lacking. There is insufficient scientific evidence to determine if vitamin E prevents colon cancer. In patients with previous colon cancer, a combination of vitamins A, C, and E has been reported to reduce the risk of developing recurrent colon cancer. Preventive benefits have also been suggested in those with no prior colon cancer when vitamin E is used in multivitamin preparations, but not when Vitamin E is used alone. Results from the Women's Health Study report no overall reduction in cancer risk with daily use of vitamin E, although this study was not large enough to look at colon cancer specifically. Additional research is necessary in this area before a firm conclusion can be reached. Caution is merited in people undergoing treatment with chemotherapy or radiation, because it has been proposed that the use of high-dose antioxidants may actually reduce the anti-cancer effects of these therapies. This remains an area of controversy and studies have produced variable results. Patients interested in using high-dose antioxidants such as vitamin E during chemotherapy or radiation should discuss this decision with their medical oncologist or radiation oncologist. Caution is advised when taking vitamin E supplements, as numerous adverse effects including an increased risk of bleeding and drug interactions are possible.

PREVENTION

There are currently no known ways to prevent familial adenomatous polyposis coli (FAP). However, early screening with a colonoscopy may reduce the risk of developing colon cancer.

Genetic counseling is available to parents. Individuals from high-risk populations, or those with family histories of FAP, may meet with genetic counselors to determine whether they carry a genetic mutation linked to FAP. Carriers can be determined through detailed family histories or by genetic testing. Known carriers of FAP may undergo genetic counseling before they conceive a child. Genetic counselors can explain the options and the associated risks of various tests, such amniocentesis, chorionic villus sampling (CVS), or preimplantation diagnosis.

AUTHOR INFORMATION

This information has been edited and peer-reviewed by contributors to the Natural Standard Research Collaboration (www.naturalstandard.com).

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