Familial Adenomatous Polyposis
What is familial adenomatous polyposis?
Familial adenomatous polyposis (FAP) is a hereditary cancer predisposition syndrome characterized by the development of hundreds of gastrointestinal polyps in the small and large intestines. The polyps are small abnormal tissue growths that develop along the lining of the intestines. If left untreated, there is nearly a 100 percent chance a person with FAP will develop colorectal cancer — likely before age 40.
FAP also increases the risk of developing cancer in other parts of the body during a person’s lifetime.
Lifetime Cancer Risk for Individuals with FAP
Body site: large intestine | lifetime risk: ~100 percent (if a complete colectomy is not performed)
Body site: small intestine | lifetime risk: 4 to 12 percent
Body site: thyroid | lifetime risk: 1 to 12 percent
Body site: liver | lifetime risk: 2 percent
Body site: pancreas | lifetime risk: 1 percent
Body site: central nervous system (brain) | lifetime risk: 1 percent
Body site: bile duct/gallbladder | lifetime risk: low, but increased
Body site: stomach | lifetime risk: less than 1 percent in Western cultures
FAP affects males and females equally, and its prevalence is reported to vary from 1 in 7,000 to 1 in 22,000 individuals. Individuals with FAP account for less than 0.5 percent of all cases of colorectal cancer.
FAP, also known as APC-associated polyposis condition, is hereditary. The risk of developing the features associated with the condition can be passed from generation to generation in a family.
Types of familial adenomatous polyposis
In addition to “classic” FAP, there are several related subtypes of the condition. Once considered separate disorders, all appear to be caused by the same gene mutation, designated the APC gene.
Gardner syndrome is characterized by the presence of multiple gastrointestinal polyps, beginning, on average, at 16 years of age. By age 35, 95 percent of individuals will have intestinal polyps. Additional tumors include: osteomas (bone tumors), dental abnormalities, soft tissue tumors, and congenital hypertrophy of the retinal pigment epithelium (CHRPE).
Turcot syndrome is associated with the presence of gastrointestinal polyps and a type of central nervous system (brain) tumor known as medulloblastoma.
Attenuated FAP (AFAP) is characterized by fewer gastrointestinal polyps (average of about 30 polyps) compared to classic FAP, but still carries a significant risk of developing colon cancer if left untreated. The average age of onset of colon cancer is about 55 years old, which is about 15 years later than average age of colon cancer onset in individuals with classic FAP.
Gastric adenocarcinoma and proximal polyposis of the stomach (GAPPS)
GAPPS is characterized by stomach polyps (gastric fundic gland polyposis), an increased risk of stomach (gastric) cancer, and limited involvement of the large intestine (colon).
Signs and symptoms of familial adenomatous polyposis
The most common symptoms of classic FAP are abdominal pain, cramping, and vomiting (with blood in the vomit) or bleeding with bowel movements secondary to the presence of 100 or more adenomatous polyps in the small and/or large intestines. However, some individuals with FAP may not have symptoms from the polyps. Individuals with FAP generally begin to develop polyps in their mid-teens; by age 35, more than 95 percent of individuals with FAP will have multiple colon polyps.
Thyroid nodules are typically not associated with symptoms but are found on exam (a lump in the front side, lower part of the neck) or by radiologic imaging (ultrasound).
Causes of familial adenomatous polyposis
FAP is caused by an alteration, also known as a “mutation," of the adenomatous polyposis coli (APC) gene on chromosome 5 at position q21. Alternatively, all or part of the FAP gene may be deleted. The condition can be inherited or caused by random mutations during prenatal development.
The role of the APC gene is to produce a protein that helps regulate cell growth, division and cell death. When one or both copies of the APC gene are altered within a cell, such as those that line the intestines, the affected cell(s) may divide in an uncontrolled fashion and acquire additional genetic alterations. If this occurs, abnormal cells may accumulate and develop into polyps and, ultimately, colon cancer.
With the exception of egg and sperm cells, each cell of our bodies normally has two working copies of the APC gene. In patients with FAP, however, each cell contains only one working APC gene copy. Although the second copy may be present, it is altered and does not function properly.
The APC gene mutation is inherited in an autosomal dominant fashion, meaning that a person carrying a mutation in one copy of the APC gene has a 50 percent chance of passing this same alteration onto each of their future children. Children who inherit the altered gene copy have FAP and have an increased risk of developing colon cancer and other features associated with FAP.
Approximately 70 percent of patients with FAP inherit an altered copy of the APC gene from a parent who also has FAP. In the remaining 30 percent of 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. Although these individuals will be the first in their family to carry the mutated gene, each of their future children will have a 50 percent chance of inheriting the same genetic alteration.
Testing and diagnosis of familial adenomatous polyposis
The diagnosis of FAP relies on the presence of certain findings, such as stomach or large intestine (colonic) polyps, and a positive family history of polyps and/or colon cancer. FAP is commonly diagnosed when an individual has one of the following features:
- 100 or more adenomatous polyps in the large and/or small intestines
- Less than 100 adenomatous polyps and a relative with a known diagnosis of FAP
If there is any indication your child may have FAP, they should be referred to a facility that has the experience, expertise and resources to fully evaluate and care for your child. At Children’s Hospital of Philadelphia, a diagnosis of FAP involves evaluation by the Cancer Predisposition Program, Gastroenterology (GI) and the Pediatric Thyroid Center.
A doctor or genetic counselor will construct a pedigree — or multi-generation family tree — that indicates which members of the family have developed certain clinical findings or cancer, taking note of the types of cancer and the ages of onset.
If the pattern of clinical features and/or cancers is suggestive of FAP, the physician or genetic counselor will recommend genetic testing be performed. The genetic test results will provide valuable information to determine if screening for additional tumors should be pursued over the lifetime of the patient, as well as for other family members.
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.
Treatment of familial adenomatous polyposis
Because all individuals with FAP develop gastrointestinal polyps, gastroenterologists often lead the treatment discussion with patients and families, and refer to other specialties — such as oncology and endocrinology — as needed.
For most individuals with FAP, treatment will eventually include surgery (colectomy) to remove all or part of the colon. This is performed as a preventative measure to reduce the risk of colon cancer and is usually performed before age 40. Most colectomies in patients with FAP are performed between late teens and late 30s.
Treatment may also include:
- Surgery to remove polyps or growths
- Investigational therapies
Follow-up care and cancer screening for familial adenomatous polyposis
Individuals with FAP will need long-term follow-up care for the rest of their lives. They have a nearly 100 percent chance of developing colorectal cancer if colon polyps are not removed and the condition is left untreated.
A diagnosis of FAP increases the risks of developing other types of tumors, so ongoing cancer screening is essential to help clinicians identify symptoms early, and treat them more effectively.
Overall, a person with FAP has a 10 to 15 percent chance of developing at least one form of cancer (other than colon cancer) during their lifetime.
Regardless of whether the parents of a child with colon polyps decide to pursue testing for APC mutations in their family, it is recommended that they consider the following surveillance measures:
- Annual physical examination by a doctor
- Sigmoidoscopy or colonoscopy to screen for colon polyps every one to two years, beginning at age 10-12, or 10 years prior to the earliest cancer diagnosis in the family. Both procedures allow for an internal examination of the colon; however, a colonoscopy looks at the entire large bowel, whereas a sigmoidoscopy examines only a specific portion of the large bowel.
- Although no hepatoblastoma (liver cancer) screening recommendations have been made for patients with FAP, the following screening recommendations for other conditions with increased risk of liver cancer and adrenal masses may be considered:
- Abdominal ultrasound examination every three months from infancy to 4-5 years old.
- Serial examination of serum alpha-fetoprotein (AFP) levels every three months from infancy to 4-5 years old. AFP is a protein released by hepatoblastoma tumors and can be a highly sensitive way to detect these cancers.
- Annual thyroid exam and thyroid ultrasound, beginning in the late teenage years. The thyroid ultrasound is better at detecting small thyroid nodules that may be missed during a physical examination alone.
Adults with FAP should pursue a healthy lifestyle, avoid tobacco use and excess alcohol consumption, maintain a healthy weight and diet, use protective measures when in the sun, and follow published guidelines for cancer surveillance. These include:
- A complete physical examination every 12 months, including evaluation for manifestations outside of the colon, usually for cosmetic concerns.
- Annual thyroid exam and thyroid ultrasound beginning in the late teenage years. The thyroid ultrasound is better at detecting small thyroid nodules that might be missed by a physical examination alone.
- Annual colonoscopy, if colectomy (removal of all or part of the colon) is delayed more than a year after polyps emerge.
- Esophagogastroduodenoscopy (EGD), which allows for visualization of the upper gastrointestinal tract, beginning by age 25, or prior to colectomy and then repeated every one to three years. The frequency of EGD depends on the severity of adenomas that are found in the stomach and/or upper intestines.
- Small-bowel imaging when adenomas are detected in the duodenum (part of the small intestine) or prior to colectomy, repeated every one to three years depending on findings and presence of symptoms.
Screening recommendations may be updated over time as new information and screening methods become available. Individuals with FAP should follow up regularly with a doctor who is knowledgeable about FAP and the most up-to-date screening recommendations.
As your child with familiar adenomatous polyposis grows into adulthood, they may consider starting a family of their own. For families that are interested, reproductive options exist for individuals with an alteration in the APC gene who do not wish to pass this alteration onto future children.
DNA is isolated from the cells of the developing baby through one of two procedures (chorionic villus sampling [CVS] or amniocentesis) and is analyzed for alterations in the APC gene. With appropriate counseling, a parent can then decide whether to carry the pregnancy to term or to end the pregnancy.
Pre-implantation genetic diagnosis (PGD)
For couples using in vitro fertilization to become pregnant, embryos can be tested for genetic disorders before transferring them into the uterus. Only healthy embryos carrying two working copies of the APC gene would be implanted.
Before one can proceed with prenatal testing or PGD, an APC mutation must be identified in a parent with familiar adenomatous polyposis.
Long-term outlook for FAP
The long-term outlook for patients with APC gene mutations is highly variable and depends on the symptoms, severity, and how quickly complications are diagnosed and treated. Life-long monitoring is highly recommended for all patients with FAP.
Children with FAP can continue to be monitored at Children’s Hospital of Philadelphia into adulthood when care will be transitioned to adult providers. Adults with FAP who live in the Greater Philadelphia region may be referred to the Gastrointestinal (GI) Cancer Risk Evaluation Program at the Hospital of the University of Pennsylvania.
Individuals with FAP have a 50 percent chance of passing along their genetic mutation to their children, so family planning should be carefully considered.
Reviewed by Garrett M. Brodeur, MD, Kristin Zelley, MS, Andrew J. Bauer, MD