Familial adenomatous polyposis (FAP) is a rare hereditary cancer syndrome associated with the development of colon cancer at an earlier than expected age. Familial adenomatous polyposis is characterized by the presence of gastrointestinal polyps, (abnormal tissue growths that develop from the lining of the large and small intestines, and less commonly, the stomach). Some of these polyps can become cancerous. Because Familial adenomatous polyposis is hereditary, the risk of developing the features associated with FAP can be passed from generation to generation in a family.
FAP is caused by alterations, also known as mutations, at specific areas within an individual’s genetic information. Each of us has a large amount of genetic information that is organized into smaller segments known as “genes.” Genes provide the necessary instructions that our cells require to perform their different functions within our bodies.
There is a specific gene known as APC, located on chromosome 5 at position q21, that is altered in patients with familial adenomatous polyposis. The normal role of the APC gene is to produce a protein that helps regulate cell growth and division and cell death. When both copies of the APC gene are altered within a cell, such as those that line the intestines, the affected cell may divide in an uncontrolled fashion and acquire additional genetic alterations. If this occurs, abnormal cells may accumulate and develop into polyps and ultimately, if left untreated, colon cancer.
With the exception of egg and sperm cells, each cell of the body normally has two working copies of the APC gene. In patients with familial adenomatous polyposis, however, each cell contains only one working APC gene copy. While the second copy is present, it is altered so that it does not function properly. A person carrying an alteration in one copy of the APC gene has a 50 percent (or 1 in 2) chance of passing this same alteration on to his or her children. Children who inherit the altered gene copy will have FAP and therefore will be at increased risk to develop colon cancer and other features associated with FAP.
Approximately 75 percent to 80 percent of patients with familial adenomatous polyposis inherit an altered copy of the APC gene from a parent who also has FAP. In the remaining patients, FAP results from the occurrence of a “new” mutation in the APC gene in one of the father’s sperm, mother’s eggs or in a cell of the developing fetus. Therefore, these individuals will be the first ones in their family to carry this genetic change. Since they carry an altered gene copy, each of their future offspring will have a 50 percent chance of inheriting the genetic alteration.
The diagnosis of familial adenomatous polyposis relies on the presence of certain findings, such as colon polyps, and a positive family history of polyps and/or colon cancer. For example, FAP is commonly diagnosed when an individual has one of the following features:
In addition to developing polyps of the gastrointestinal tract, patients with familial adenomatous polyposis may also develop:
It is important to note that patients with familial adenomatous polyposis are at increased risk to develop other types of cancer in addition to cancer of the colon or stomach. For example, patients with FAP can develop soft tissue tumors known as desmoid tumors and, less commonly, cancers of the liver, thyroid, pancreas, brain and bile ducts (tubes that drain the gall bladder). Overall, the incidence of these other cancers is 10 percent to 15 percent in patients with FAP.
In addition to familial adenomatous polyposis, there are three related conditions that are also caused by alterations in the APC gene. These conditions are now considered to be variants of familial adenomatous polyposis. These include:
Recently, another hereditary syndrome known as MYH-associated polyposis (MAP) was described in which affected individuals carry alterations in both copies of the MYH gene. MAP shares many clinical features with FAP including:
Some groups have reported an increased risk to develop other malignancies that are NOT typically associated with FAP, including ovarian cancer, bladder cancer, and possibly breast and endometrial cancer (Lindor, 2009; Vogt et al., 2009). However, the risk to develop these cancers has not been well-characterized for individuals with MAP.
A careful and detailed review of an individual’s medical and family history is important in diagnosing an APC-associated polyposis condition. A doctor or genetic counselor may construct a pedigree, or a multi-generation family tree, that indicates:
If the pattern of clinical features and/or cancers is suggestive of an APC-associated polyposis condition, the physician or counselor may recommend that genetic testing be performed.
Even in cases where an individual does not meet all of the diagnostic criteria for FAP, it may still be recommended that an affected individual undergo genetic testing to investigate for the presence of an APC gene alteration.
Because FAP shares features with MAP, additional genetic testing to investigate for alterations in the MYH gene may be recommended if no alteration is identified in the APC gene.
In order to confirm on a molecular level that an individual has FAP, he or she can undergo the process of genetic testing:
It is important to remember that not all patients with FAP carry a detectable alteration in the APC gene. Therefore, the failure to identify an alteration in the APC gene does not exclude a diagnosis of FAP.
APC genetic test results can also provide important information for other family members. Knowing the specific alteration that is present in an individual with FAP allows for other family members to undergo testing to determine whether they also carry the alteration and could therefore develop the features of FAP.
Reproductive options exist for an individual with an alteration in the APC gene who does not wish to pass this alteration on to future children:
Individuals carrying an alteration in one copy of the APC gene are born and develop normally, but they are at an increased risk to develop polyps in the gastrointestinal tract, particularly in the colon. These polyps often begin to develop by the age of 16 years (range 7 to 36 years). By the age of 35 years, up to 95 percent of patients with FAP have developed polyps in the colon and, without removal of the colon, patients will undoubtedly develop colon cancer. The average age of colon cancer diagnosis in untreated patients with FAP is 39 years (age 34 to 43 years).
Individuals with familial adenomatous polyposis are also at increased risk to develop benign and malignant tumors outside of the gastrointestinal tract. These can include:
Some cancers that do not involve the colon have a slightly increased incidence in individuals with Familial Adenomatous Polyposis as compared to individuals without FAP. A person with FAP has the following lifetime risks of developing these other cancers:
Regardless of whether the parents of a child with polyps decide to pursue testing for APC mutations in their family, it is recommended that they consider the following surveillance measures, which are based on information listed on the www.genetests.org Web site.
For children, recommended surveillance measures include:
Children should be encouraged to lead as healthy a lifestyle as possible. They should eat a balanced diet, avoid excess sun exposure and always wear sun block and a hat when outdoors in the sunlight. As adolescents, they should be discouraged from smoking cigarettes or cigars and should not be exposed second hand smoke. Parents should watch for symptoms of illness and have their children evaluated promptly if these occur.
Adults within the family should pursue a healthy lifestyle, avoid tobacco use and excess alcohol consumption, use protective measures when in the sun and follow published guidelines for cancer surveillance, which include:
We recommend that children with a diagnosis of familial adenomatous polyposis, or those suspected of having familial adenomatous polyposis, contact the Division of Gastroenterology, Hepatology and Nutrition at The Children's Hospital of Philadelphia to discuss issues related to the management of this condition. Please call 215-590-3630 to schedule an appointment.
Adults who have familial adenomatous polyposis or who would like more information about familial adenomatous polyposis may contact the Gastrointestinal (GI) Cancer Risk Evaluation Program at the Hospital of the University of Pennsylvania by calling the coordinator, Samatha Halter, at 215-898-0154 or email@example.com.
American Cancer Society (for information on regional support)
1599 Clifton Road NE
Atlanta, Ga 30329
C3: Colorectal Cancer Coalition
1414 Price Street
Alexandria, VA 222314
Colon Cancer Alliance
1200 G Street, NW
Washington, DC 20005
Genetic and Rare Diseases Information Center (GARD) — Familial Adenomatous Polyposis
National Cancer Institute -- Genetics of Colorectal Cancer
National Library of Medicine Genetics Home Reference -- Familial adenomatous polyposis
GeneReviews -- APC-Associated Polyposis Conditions
Lindor, N.M. (2009). Hereditary-colorectal cancer: MYH-associated polyposis and other newly-identified disorders. Best Practices & Research Clinical Gastroenterology, 23, 75-87.
Lynch, H.T., Smyrk, T., McGinn, T., Lanspa, S., Cavalieri, J., Lynch, J., Slominski-Castor, S., Cayouette, M.C., Priluck, I., & Luce, M.C. (1995). Attenuated familial adenomatous polyposis (AFAP): A phenotypically and genotypically distinctive variant of FAP. Cancer, 76, 2427-2433.
Vogt, S., Jones, N., Christian, D., Engel, C., Nielsen, M., Kaufmann, A., Steinke, V., Vasen, H.F., Propping, P., Sampson, J.R., Hes, F.J., & S. Aretz. (2009). Expanded extracolonic tumor spectrum in MUTYH-associated polyposis. Gastroenterology, 137, 1976-1985.
Reviewed by: Kim Nichols, MD, Kristin Zelley, MS
Date: September 2012