What is familial adenomatous polyposis?
Familial adenomatous polyposis is an inherited cancer syndrome that predisposes patients to early-onset colorectal cancer, and some other cancers.
- Familial adenomatous polyposis is very rare, affecting 1 in 7,000 people.
- It causes less than 1 per cent of all colorectal cancer cases.
- The average age of onset is 39 years.
- Some individuals have a variant of the disorder called attenuated familial adenomatous polyposis where onset of the symptoms is delayed. The average age for this is 55 years.
- Caused by mutations in the adenomatous polyposis coli (APC) gene on chromosome 5.
- Many mutations in the APC gene have been identified.
- Familial adenomatous polyposis is a dominant genetic disease. This means that only one copy of the mutated APC gene is needed for the individual to have the syndrome.
- Each child born to a person with familial adenomatous polyposis has a 50 per cent chance of inheriting the mutated gene (many people with familial adenomatous polyposis are diagnosed because they have an affected relative).
- APC is a tumour suppressor gene which means that, when functioning normally, it stops irregular cell growth to prevent tumours from forming.
- A mutation in the APC gene affects the ability of a cell to maintain normal growth and function so the cells grow out of control.
- This cell overgrowth leads to the formation of colorectal polyps, characteristic of familial adenomatous polyposis.
- There is a high risk that these polyps will then develop a mutation in the second copy of their APC gene (the first copy is already mutated to cause the syndrome in the first place), causing cancer.
- Although most people with mutations in the APC gene will go on to develop colorectal cancer, the number of polyps and time frame in which they become cancerous depends on the location of the genetic mutation.
- If left untreated, almost all people with familial adenomatous polyposis will develop colorectal cancer by the time they are 50 years old.
- 7 per cent of patients will develop colorectal cancer by age 21
- 87 per cent of patients will develop colorectal cancer by age 45
- 93 per cent of patients will develop colorectal cancer by age 50
- Typically if left untreated patients will develop colorectal cancer between 34 and 43 years.
- The risk of developing colorectal cancer in these people is so high that they are often advised by their doctor to have their large bowel surgically removed before they reach the age of 25.
- During their teens and twenties individuals with familial adenomatous polyposis develop many protruding, non-cancerous growths in their colon (known as adenomatous colorectal polyps).
- The more polyps a patient has, the higher the chance of cancer developing.
- Prior to polyps forming, the disease usually shows no symptoms (is asymptomatic). This is usually in patients under the age of 10 years.
- Common symptoms of polyp formation and colorectal cancer are:
- rectal bleeding
- tummy pain
- bony growths
- common cancer-related symptoms such as unexplained weight loss and fatigue.
- Duodenal polyps may also occur in people with familial adenomatous polyposis, but usually at an older age (over 30 years).
- Generally, familial adenomatous polyposis is suspected if there is a history of the disease in the family at a young age.
- To be diagnosed with the condition, patients have to have more than 100 colorectal polyps in their colon and rectum and a relative with confirmed familial adenomatous polyposis.
- A flexible colonoscopy (when a bendy camera, called an endoscope, is inserted up the bottom to look at all parts of the large intestine, including the rectum and colon) is used to monitor patients annually from their mid-teens.
- The upper gastrointestinal tract can also be checked for polyps using an endoscope inserted down the throat.
- Genetic testing is also used to help diagnose patients with the condition and genetic counselling is provided for those who receive a positive result.
- To remove the risk of cancer in people with familial adenomatous polyposis, most choose to have surgery to remove their colon during their late teens or early twenties before cancer has a chance to develop.
- Direct visualisation and surveillance for duodenal polyps should start at around 25 to 30 years, and be repeated every 1 or 2 years. This is done via an endoscope that is inserted through the mouth while the patient is sedated.
- Small polyps are removed using an endoscope but large or cancerous polyps need to be removed surgically.
- Lifelong follow-up is required to ensure that other cancerous polyps are caught as early as possible.
This page was last updated on 2021-07-21