What is Familial Adenomatous Polyposis?

Familial Adenomatous Polyposis is a condition that mostly affects the digestive system. People with Familial Adenomatous Polyposis typically develop abnormal tissue growths in the large and small intestines. These growths are called polyps. If not removed, some of these polyps can become cancerous over time. For this reason, people with Familial Adenomatous Polyposis are at high risk to develop colon cancer and other digestive system cancers at a young age.

Besides polyps, people with Familial Adenomatous Polyposis are at increased risk to develop other tumors or cancers, and they may have other medical issues.

Familial Adenomatous Polyposis is hereditary, which means it can be passed from parents to their children.

There are four subtypes of Familial Adenomatous Polyposis:

  • Classic Familial Adenomatous Polyposis: People with this subtype usually develop at least 100 polyps, but usually many more, in the large and small intestines by the time they are adults.
  • Attenuated Familial Adenomatous Polyposis (AFAP): People with this subtype have fewer polyps in the large and small intestines, usually no more than 30 by the time they are adults.
  • Gardner Syndrome: People with this subtype have the polyps seen in classic Familial Adenomatous Polyposis, plus osteomas, epidermal cysts, fibromas, and desmoid tumors.
  • Turcot Syndrome: People with this subtype have the polyps seen in classic Familial Adenomatous Polyposis, plus a type of brain tumor known as medulloblastoma.

Familial Adenomatous Polyposis is caused by changes in a gene known as APC. Genes carry information telling cells in the body how to work. The APC gene helps to control how and when cells grow, divide, and die.

Most people without Familial Adenomatous Polyposis carry two working copies of the APC gene in their cells. One copy is inherited from each parent. Cells from people with Familial Adenomatous Polyposis carry one working copy of APC and one copy that is changed. This change causes the gene to not work right. It is called an APC variant.

Most children with Familial Adenomatous Polyposis inherit the APC gene variant from a parent who also has the syndrome, although about 20% to 25% of people with Familial Adenomatous Polyposis have a new APC variant that did not come from a parent. These children have no history of the syndrome in their family. In these cases, the change either happened in an egg or sperm cell when the child was formed or in one of the child’s cells during pregnancy. These children are the first in their families to have Familial Adenomatous Polyposis. No matter how they acquired the APC variant, people with Familial Adenomatous Polyposis have a 50% (or 1 in 2) chance of passing it on to their children.

As people with Familial Adenomatous Polyposis get older, the remaining working copy of APC often becomes changed in some of their cells. When both copies of the gene are changed, cancer can develop. That is why people with Familial Adenomatous Polyposis have a higher risk of developing cancer than people who do not have this condition.

A doctor may suspect this diagnosis after looking at a person’s medical or family history. In most cases, a doctor or genetic counselor will ask questions about the person’s health and the health of other family members. Read more about genetic counseling and genetic testing.

Diagnosing this syndrome is usually done by sequencing the APC gene to find variants (changes in the gene).

The major cancer risk in Familial Adenomatous Polyposis is cancer in the large and small intestines. For people with classic Familial Adenomatous Polyposis, Gardner Syndrome, and Turcot Syndrome, polyps in the colon often start appearing around age 16. They can appear as early as 7 years old or as late as 35.

By age 35, about 95% of people with these conditions have developed polyps in the colon. Without surgery to remove the colon, people with these types of Familial Adenomatous Polyposis will all eventually develop colon cancer. The average age of colon cancer in people with Familial Adenomatous Polyposis who have not had their colon removed is around 39 years old.

People with classic Familial Adenomatous Polyposis, Gardner Syndrome, and Turcot Syndrome are also at risk for small intestine cancer. The lifetime risk of small intestine cancer is 4% to 12%. Small intestine cancer usually occurs after age 17. The average age of diagnosis is between 45 and 52 years.

For people with attenuated Familial Adenomatous Polyposis, the lifetime risk of colon cancer is about 70%. For those with this subtype who have not had their colon removed, the average age of colon cancer diagnosis is 50 to 55 years.

People with Familial Adenomatous Polyposis are also at risk for the following kinds of cancer:

  • Thyroid cancer. The risk of thyroid cancer is higher in females with Familial Adenomatous Polyposis (1-12%).
  • Hepatoblastoma, a liver cancer most often seen in children under the age of 4. The risk of hepatoblastoma in children is less than 2%.
  • Medulloblastoma, a brain cancer that also typically occurs in childhood. The risk of medulloblastoma is less than 1%.

Cancer screening involves tests to check for cancer before symptoms occur. The goal is to find cancer at the earliest and most treatable stage. Guidelines for cancer screening are available online. Recommended screenings may change over time as doctors learn more about this syndrome, so these screening tests should be discussed with a health care provider who knows this syndrome well.

Familial Adenomatous Polyposis is one of the only cancer predisposition syndromes that has a treatment available to prevent cancer. The treatment involves removing polyps and, eventually, the colon. This treatment can greatly reduce or even eliminate the risk of developing colon cancer.

Other ideas to reduce the risk of cancer include:

  • Eat a healthful diet with lots of fruits and vegetables
  • Get regular exercise
  • Avoid smoking or using tobacco products
  • Avoid secondhand smoke
  • Avoid excess sun exposure and always wear sunscreen, hat, and protective clothing when out in the sun
  • Get medical attention for unusual or ongoing symptoms

People with Familial Adenomatous Polyposis may have additional medical issues, including congenital hypertrophy of the retinal pigment epithelium (or CHRPE, changes in the appearance of the inside of the eye), epidermoid cysts and fibromas (non-cancerous growths under the skin), desmoid tumors (non-cancerous tumors in the soft tissues, usually in the abdomen), osteomas (non-cancerous growths of the bones), dental problems (teeth that do not erupt through the gums, extra or missing teeth, cysts), or adrenal tumors (non-cancerous tumors in the small organ on top of each kidney).

Because of the other medical issues related to this syndrome, specialists in the following areas may need to assess a child with Familial Adenomatous Polyposis:

  • Gastroenterology
  • Surgery
  • Ophthalmology
  • Dermatology
  • Dentistry

Resources about Familial Adenomatous Polyposis:

Other resources: