Familial adenomatous polyposis
Medically reviewed by Drugs.com. Last updated on Jun 30, 2021.
Familial adenomatous polyposis (FAP) is a rare, inherited condition caused by a defect in the adenomatous polyposis coli (APC) gene. Most people inherit the gene from a parent. But for 25 to 30 percent of people, the genetic mutation occurs spontaneously.
FAP 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 when you are in your 40s.
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 by removing polyps regularly.
Some people have a milder form of the condition, called attenuated familial adenomatous polyposis (AFAP). People with AFAP usually have fewer colon polyps (an average of 30) and develop cancer later in life.
The main sign of FAP is hundreds or even thousands of polyps growing 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 is caused by a defect in a gene that's usually inherited from a parent. But some people develop the abnormal gene that causes the condition.
Your risk of familial adenomatous polyposis is higher if you have a parent, child, brother, or sister with the condition.
In addition to colon cancer, 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.
- Gastric fundic polyps. These polyps grow in the lining of your stomach.
- 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 (benign) skin tumors.
- Benign bone growths (osteomas).
- Congenital hypertrophy of the retinal pigment epithelium (CHRPE). These are benign pigment changes in the retina of your eye.
- Dental abnormalities. These include extra teeth or teeth that don't come in.
- Low numbers of red blood cells (anemia).
Preventing FAP is not possible, since it is an inherited genetic condition. However, if you or your child is at risk of FAP because of a family member with the condition, you will need genetic testing and counseling.
If you have FAP, you will need regular screening, followed by surgery if needed. Surgery can help prevent the development of colorectal cancer or other complications.
You're at risk of familial adenomatous polyposis if you have a parent, child, brother or sister with the condition. If you're at risk, it's important to be screened frequently, starting in childhood. Annual exams can detect the growth of polyps before they become cancerous.
- Sigmoidoscopy. A flexible tube is inserted into your rectum to inspect the rectum and sigmoid — the last two feet of the colon. For people with a genetic diagnosis of FAP or family members at risk who haven't had genetic testing, the American College of Gastroenterology recommends annual sigmoidoscopy, beginning at ages 10 to12 years.
- Colonoscopy. A flexible tube is inserted into your rectum to inspect the entire colon. Once polyps are found in your colon, you need to have an annual colonoscopy until you have surgery to remove your colon.
- Esophagogastroduodenoscopy (EGD) and side-viewing duodenoscopy. Two types of scopes are used to inspect your esophagus, stomach and upper part of the small intestine (duodenum and ampulla). The doctor may remove a small tissue sample (biopsy) for further study.
- CT or MRI. Imaging of the abdomen and pelvis may be used, especially to evaluate desmoid tumors.
A simple blood test can determine if you carry the abnormal gene that causes FAP. Genetic testing may also detect whether you're at risk of complications of FAP. Your doctor may suggest genetic testing if:
- You have family members with FAP
- You have some, but not all, of the signs of FAP
Ruling out FAP spares at-risk children years of screening and emotional distress. For children who do carry the gene, appropriate screening and treatment greatly reduce the risk of cancer.
Your doctor may recommend thyroid exams and other tests to detect other medical problems that can occur if you have FAP.
At first, your doctor will remove any small polyps found during your colonoscopy exam. Eventually, though, the polyps will become too numerous to remove individually, usually by your late teens or early 20s. Then you will need surgery to prevent colon cancer. You will also need surgery if a polyp is cancerous. You may not need surgery for AFAP.
Minimally invasive colorectal surgery
Your surgeon may decide to perform your surgery laparoscopically, through several small incisions that require just a stitch or two to close. This minimally invasive surgery usually shortens your hospital stay and allows you to recover more quickly.
Depending on your situation, you may have one of the following types of surgery to remove part or all of the colon:
- Subtotal colectomy with ileorectal anastomosis, in which the rectum is left in place
- Total proctocolectomy with a continent ileostomy, in which the colon and rectum are removed and an opening (ileostomy) is created, usually on the right side of your abdomen
- Total proctocolectomy with ileoanal anastomosis (also called J-pouch surgery), in which the colon and rectum are removed and a part of the small intestine is attached to the rectum
Surgery doesn't cure FAP. Polyps can continue to form in the remaining or reconstructed parts of your colon, stomach and small intestine. Depending on the number and size of the polyps, having them removed endoscopically may not be enough to reduce your risk of cancer. You may need additional surgery.
You will need regular screening — and treatment if needed — for the complications of familial adenomatous polyposis that can develop after colorectal surgery. Depending on your history and the type of surgery you had, screening may include:
- Sigmoidoscopy or colonoscopy
- Upper endoscopy
- Thyroid ultrasound
- CT or MRI to screen for desmoid tumors
Depending on your screening results, your doctor may additional treatments for the following issues:
- Duodenal polyps and periampullary polyps. Your doctor may recommend surgery to remove the upper part of the small intestine (duodenum and ampulla) because these types of polyps can progress to cancer.
- Desmoid tumors. You may be given a combination of medications, including nonsteroidal anti-inflammatory drugs, anti-estrogen and chemotherapy. In some cases, you may need surgery.
- Osteomas. Doctors may remove these noncancerous bone tumors for pain relief or cosmetic reasons.
Potential future treatments
Researchers continue to evaluate additional treatments for FAP. In particular, the use of pain relievers such as aspirin and nonsteroidal anti-inflammatory drugs (NSAIDs), as well as a chemotherapy drug, are being investigated.
Coping and support
Some people find it helpful to talk with others who share similar experiences. Consider joining an online support group, or ask your doctor about support groups in your area.
Preparing for an appointment
What you can do
Your time with your doctor may be limited, so try to prepare a list of questions. For FAP, some basic questions to ask your doctor may include:
- What are the chances that I will pass the condition on to my children?
- How often will I need to have screening?
- What kind of tests will my screening involve?
- Will I need surgery?
- If I need surgery, when will I need it?
- What kind of surgery will I need?
- Will surgery cure my FAP?
- If not, what follow-up and treatment will I need?
- How accurate is genetic testing?