Familial Adenomatous Polyposis

Approved by the Lineagotica Editorial Board, 05/2017

Classic familial adenomatous polyposis, called FAP or classic FAP, is a genetic condition. It is diagnosed when a person develops more than 100 adenomatous colon polyps. An adenomatous polyp is an area where normal cells that line the inside of a person’s colon form a mass on the inside of the intestinal tract. The average age for polyps to develop in people with FAP is in the mid-teens. Most people with FAP will have multiple colon polyps by age 35. If FAP is not recognized and treated, there is a very high likelihood that a person will develop colorectal cancer.

Individuals with FAP also have an increased chance of developing cancer in other organs, including the stomach, small intestine, and the pancreas and biliary tree. Risk for hepatoblastoma, a type of liver cancer, is increased in children with FAP. Desmoid tumors/desmoid fibromatosis, a locally aggressive tumor that does not spread (metastasize) and a type of brain tumor called medulloblastoma can also occur in some individuals. Risk for papillary thyroid cancer is also increased.

Not all symptoms of FAP are cancer-related. Some additional features of FAP may include:

  • Osteomas, which are noncancerous bony growths, usually found on the jaw

  • Extra, missing, or unerupted teeth

  • Congenital hypertrophy of the retinal pigment epithelium (CHRPE). This is an eye condition that is present at birth that does not affect vision, but it is a condition that an eye doctor may see during an examination with a special instrument called an ophthalmoscope.

  • Benign (noncancerous) skin changes, such as epidermoid cysts and fibromas

  • Adrenal masses

Are there subtypes of classic FAP?

There are 3 subtypes of classic FAP: attenuated FAP (AFAP), Gardner syndrome, and Turcot syndrome.

  • AFAP. People with AFAP will also have an increased number of adenomatous colon polyps during their lifetime and an increased risk of developing colorectal cancer. However, in AFAP, the total number of colon polyps is less than in classic FAP, typically fewer than 100. Polyps in people with AFAP tend to develop later in life than in individuals with classic FAP.

    AFAP is still being defined by doctors. It has not been determined if families with AFAP have the same risk for other types of cancer, in addition to colon cancer, as families with classic FAP. Similarly, risks for some of the other, noncancerous features associated with classic FAP have not been determined fully.

  • Gardner syndrome. Gardner syndrome is a variant of FAP. Like in FAP, people with Gardner syndrome develop multiple adenomatous colon polyps, but in addition, they also develop other tumors outside the gastrointestinal organs, which may include:

    • Epidermoid cysts, which are lumps in or under the skin

    • Fibromas, which are fibrous tumors

    • Desmoid tumors, which are fibrous tumors that can develop anywhere in the body

    • Osteomas, which are lumps in or on bone

  • Turcot syndrome. Turcot syndrome is considered a variant of either FAP or Lynch syndrome, rather than a distinct genetic condition by itself.

    People with Turcot syndrome also have multiple adenomatous colon polyps, an increased risk of colorectal cancer, and an increased risk of brain tumors. The type of brain tumor generally depends on whether the Turcot syndrome is more similar to Lynch syndrome or more similar to FAP. The 2 most common types of brain tumors in Turcot syndrome are:

    • Glioblastoma. This type of brain tumor is a very aggressive form of astrocytoma that is commonly found in families who have features of Lynch syndrome.

    • Medulloblastoma. This type of brain tumor begins in the cerebellum, the back of the brain. Medulloblastoma most often occurs in children and is commonly found in families who have features of FAP.

What causes classic FAP and its subtypes?

FAP is passed from generation to generation in a family. The APC gene is linked to FAP, AFAP, Gardner syndrome, and Turcot syndrome. APC stands for adenomatous polyposis coli. A mutation (alteration) in the APC gene gives a person an increased lifetime risk of developing colorectal cancer or other cancers of the digestive tract. 

Some individuals with colon polyposis are found to carry mutations in the MUTYH gene, also called the MYH gene, that is associated with MYH-Associated Polyposis (MAP).

How are classic FAP and its subtypes inherited?

Normally, every cell has 2 copies of each gene: 1 inherited from the mother and 1 inherited from the father. FAP follows an autosomal dominant inheritance pattern. In autosomal dominant inheritance, a mutation happens in only 1 copy of the gene. This means that a parent with a gene mutation may pass along a copy of their normal gene or a copy of the gene with the mutation. Therefore, a child who has a parent with a mutation has a 50% chance of inheriting that mutation. A brother, sister, or parent of a person who has a mutation also has a 50% chance of having the same mutation. 

Options exist for people interested in having a child when a prospective parent carries a gene mutation that increases the risk for a hereditary cancer syndrome. Preimplantation genetic diagnosis (PGD) is a medical procedure done in conjunction with in-vitro fertilization (IVF). It allows people who carry a specific known genetic mutation to reduce the likelihood that their children will inherit the condition.  A woman’s eggs are removed and fertilized in a laboratory. When the embryos reach a certain size, 1 cell is removed and is tested for the hereditary condition in question. The parents can then choose to transfer embryos which do not have the mutation. PGD has been in use for over two decades, and has been used for several hereditary cancer predisposition syndromes.  However, this is a complex procedure with financial, physical, and emotional factors to consider before starting. For more information, talk with an assisted reproduction specialist at a fertility clinic. 

How common is classic FAP and its subtypes?

FAP and AFAP are uncommon. Specific estimates on how many people have FAP vary from 1 in 22,000 up to 1 in 7,000. Approximately 30% of people with FAP do not have any family history of the condition and are the first person in their family to be affected with the condition.

Most colorectal cancer is sporadic, meaning it occurs by chance, and is not related to FAP or other inherited syndromes. Less than 1% of all colorectal cancer is thought to be due to FAP.

Gardner syndrome and Turcot syndrome are both considered to be rare.

How is classic FAP and its subtypes diagnosed?

Classic FAP is a clinical diagnosis. This means that it is typically diagnosed when the doctor finds many polyps, rather than by the results of a laboratory test. A person with more than 100 adenomatous colon polyps is considered to have FAP.

AFAP is suspected when a person has a history of more than 20, but fewer than 100, adenomatous colon polyps.

Gardner syndrome is suspected when a person has a multiple adenomatous colon polyps and/or colorectal cancer along with some of the benign tumors listed above.

Turcot syndrome is suspected when a person has multiple adenomatous colon polyps and/or colorectal cancer, along with either a glioblastoma or medulloblastoma brain tumor.

Blood tests are available to look for a mutation in the APC gene and/or MUTYH gene if FAP or its subtypes are suspected. If a gene mutation is found, other family members may be diagnosed with FAP or its subtypes if they are tested and have the same gene mutation.

What are the estimated cancer risks associated with classic FAP and its subtypes?

  • Colorectal cancer                                            up to 100% if not treated

  • Desmoid tumor                                               10% to 20%

  • Small bowel (intestines)                                 4% to 12%

  • Pancreatic cancer                                            2%

  • Papillary thyroid cancer                                  2% to 25%

  • Hepatoblastoma                                              1.5%

  • Brain or central nervous system tumor           less than 1%

  • Stomach cancer                                               0.5%

  • Bile duct cancer                                              small, but increased

  • Adrenal gland cancer                                      small, but increased

The risks of cancer for people with Turcot syndrome depend on whether it appears to be more similar to Lynch syndrome or FAP. Visit the Lynch syndrome section on this website for a summary of cancer risk and other features.

What are the screening options for classic FAP and its subtypes?

ASCO recommends the following screening for people with FAP. It is important to discuss these options with your health care team, as each individual is different:

  • Sigmoidoscopy or colonoscopy every 1 to 2 years, starting at age 10 to 11 for people with FAP and beginning at age 18 to 20 for people with AFAP.

  • Yearly colonoscopy once polyps are found until a colectomy is planned. A colectomy is the surgical removal of the entire colon. People with classic FAP may need a colectomy, due to a high number of polyps and the high risk of colorectal cancer. This is a major surgery and possible side effects may include the need for a colostomy. Talk with your health care team about what to expect during and after this surgery.

  • After colon surgery, doctors will monitor the patient’s lower tract with sigmoidoscopy, and this surveillance should continue with regular frequency, depending on type of surgery.

    Upper endoscopy(EGD) at age 25 to 30, or once colorectal polyps are found, whichever occurs first

    • every 6 to 12 months if some rectal tissue remains

    • every 1 to 4 years if all rectal tissue has been removed and there is a small intestinal pouch

  • Yearly ultrasound of the thyroid may be considered starting at age 25 to 30

  • Computed tomography (CT) scan or magnetic resonance imaging (MRI) if a person has a personal or family history of desmoid tumors

The screening options for Gardner syndrome are considered to be similar to those for classic FAP, with the addition of regular skin examinations by a dermatologist, which is a doctor who specializes in diseases and conditions of the skin.  The screening options for Turcot syndrome are considered to be similar to those for Lynch syndrome or FAP, with the addition of screening for a brain tumor.

Screening options may change over time as new technologies are developed and more is learned about FAP and its subtypes. It is important to talk with your health care team about appropriate screening tests.

Learn more about what to expect when having common tests, procedures, and scans, and read more about these screening recommendations at the Journal of Clinical Oncology. Please note this link takes you to another ASCO website.

Questions to ask the health care team

If you are concerned about your risk of colorectal cancer or other types of cancer, talk with your health care team. Consider asking the following questions:

  • What is my risk of developing colorectal cancer?

  • How many colon polyps have I had in total?

  • What kind of colon polyps have I had? The 2 most common kinds are hyperplastic and adenomatous.

  • What is my risk of developing another type of cancer?

  • What can I do to reduce my risk of cancer?

  • What are my options for cancer screening and prevention?

If you are concerned about your family history and think your family may have FAP or one of its subtypes, consider asking the following questions:

  • Does my family history increase my risk of colorectal cancer?

  • Should I meet with a genetic counselor?

  • Should I consider genetic testing?

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