Familial Adenomatous Polyposis
(FAP) and Colorectal Cancer
Familial adenomatous polyposis (FAP) is a hereditary syndrome in which hundreds to thousands of polyps grow inside
the colon and rectum. These polyps usually start to form during the teenage years. If left untreated, they almost
always turn into colorectal cancer.
Familial Adenomatous Polyposis (FAP) and Colorectal Cancer
Familial adenomatous polyposis (FAP) is a hereditary syndrome in which hundreds to thousands of polyps grow inside the colon and rectum. These polyps usually start to form during the teenage years. If left untreated, they almost always turn into colorectal cancer.
Risk of having FAP
If you have FAP and you have not had a colectomy, the average age colon cancer develops is 39. If you have had a colectomy, the risk for colon cancer is significantly reduced. But, your risk will depend on the type of colectomy and if the rectum is left in place.
For 25% to 30% of people with FAP, the condition is not inherited from a parent, and there is no family history of it.
As with other genetic conditions, you can have a hereditary syndrome without a clear explanation to how or why you have it. Regardless of whether or not FAP has been passed down in the family, a person with FAP has a 50% chance to pass on the condition to their children.
Risk of having FAP
For individuals who have not had a colectomy, the average age that colon cancer develops is 39. If a person has had a colectomy, the risk for colon cancer is significantly reduced. But, their risk will depend on the type of colectomy and if the rectum is left in place.
For 25% to 30% of people with FAP, the condition is not inherited from a parent, and there is no family history of it.
As with other genetic conditions, you can have a hereditary syndrome without a clear explanation to how or why you have it. Regardless of whether or not FAP has been passed down in the family, a person with FAP has a 50% chance to pass on the condition to their children.
What causes of FAP?
A mutation or defect in the adenomatous polyposis coli (APC) gene causes FAP. The APC gene is responsible for making the instructions for the APC protein. When the APC protein is working properly, its role is to keep cells in line or under control, which prevents tumors from forming.
Although most people with mutations in the APC gene will develop colorectal cancer if they have not had a colectomy, the number of polyps and how quickly they turn into cancer depends on some factors, such as the location and mutation of the APC gene.
Occurring in approximately 1 in 10,000 people, FAP affects both males and females equally. It is responsible for less than 1% of cases of colorectal cancer.
For people with a parent, child, or sibling with FAP, their risks of having FAP is up to 50%. Since FAP is due to a gene mutation that is present at birth, it can’t be prevented. However, preventive surgery like colectomy can significantly reduce colorectal cancer risk, and increased screening can allow for earlier detection of other cancers.
Did I have FAP from birth?
You are born with FAP, it’s not a condition that develops over time. But, the increased risk for cancer and symptoms develops over time.
As more polyps form, they may cause the same symptoms as colorectal cancer, such as:
Other symptoms of FAP can include:
If you have FAP, it’s extremely important to proactively develop a screening schedule with your doctor and notify them of any symptoms. FAP patients have an extremely high risk of developing colorectal cancer at a younger age. They are also at increased risk of developing several other cancers (stomach, small intestine, pancreas, bile duct, liver, adrenal gland, thyroid, and brain).
What causes FAP?
A mutation or defect in the adenomatous polyposis coli (APC) gene causes FAP. The APC gene is responsible for making the instructions for the APC protein. When the APC protein is working properly, its role is to keep cells in line or under control, which prevents tumors from forming.
Although most people with mutations in the APC gene will develop colorectal cancer if they have not had a colectomy, the number of polyps and how quickly they turn into cancer depends on some factors, such as the location and mutation of the APC gene.
Occurring in approximately 1 in 10,000 people, FAP affects both males and females equally. It is responsible for less than 1% of cases of colorectal cancer.
For people with a parent, child, or sibling with FAP, their risks of having FAP is up to 50%. Since FAP is due to a gene mutation that is present at birth, it can’t be prevented. However, preventive surgery like colectomy can significantly reduce colorectal cancer risk, and increased screening can allow for earlier detection of other cancers.
Did I have FAP from birth?
You are born with FAP, it’s not a condition that develops over time. But, the increased risk for cancer and symptoms develops over time.
As more polyps form, they may cause the same symptoms as colorectal cancer, such as:
Other symptoms of FAP can include:
If you have FAP, it’s extremely important to proactively develop a screening schedule with your doctor and notify them of any symptoms. FAP patients have an extremely high risk of developing colorectal cancer at a younger age. They are also at increased risk of developing several other cancers (stomach, small intestine, pancreas, bile duct, liver, adrenal gland, thyroid, and brain).
Colorectal cancer screening if you have FAP
Here is what’s recommended for screening if you have FAP. As FAP also increases the risk for other cancers, additional screenings to look at the stomach and small bowel are also recommended.
- A high-quality colonoscopy every 12 months beginning at age 10–15.
- Once polyps are found in the colon, an annual colonoscopy is recommended until/unless surgery to remove the colon takes place.
- An annual colonoscopy is recommended if a colectomy is delayed.
Surgery
Not everyone with FAP will undergo surgery; however, it’s a recommended step for most patients. Some people with FAP have undergone a prophylactic subtotal colectomy and others have had a total colectomy to prevent colorectal cancer from developing.
Your age, family history, polyp number, and precancerous changes in the polyps can all determine when and if surgery will take place. While some individuals with FAP may be in their 20s or 30s when their doctor recommends colectomy, others may be in their teens.
While colectomy may feel extreme, here are some reasons doctors recommend it:
Colorectal cancer screening if you have FAP
Here is what’s recommended for screening if you have FAP. As FAP also increases the risk for other cancers, additional screenings to look at the stomach and small bowel are also recommended.
A high-quality colonoscopy every 12 months beginning at age 10–15.
Once polyps are found in the colon, an annual colonoscopy is recommended until/unless surgery to remove the colon takes place.
An annual colonoscopy is recommended if a colectomy is delayed.
Surgery
Not everyone with FAP will undergo surgery; however, it’s a recommended step for most patients. Some people with FAP have undergone a prophylactic subtotal colectomy and others have had a total colectomy to prevent colorectal cancer from developing.
Your age, family history, polyp number, and precancerous changes in the polyps can all determine when and if surgery will take place. While some individuals with FAP may be in their 20s or 30s when their doctor recommends colectomy, others may be in their teens.
While colectomy may feel extreme, here are some reasons doctors recommend it:
Do I need genetic counseling or genetic testing for FAP?
Since FAP is a hereditary syndrome, you should strongly consider genetic counseling. A genetic counselor can explain and educate about FAP and what it means for you and your family.
Importantly, your counselor will review cancer risks and screening recommendations for FAP and the benefits of doing increased screening starting at a younger age. Genetic testing, which can be done through a saliva or blood test, may be offered.
While genetic counselors help individuals consider all of their options and choices, the patient always has the final decision.
A genetic counselor can also explain how your personal health history may impact your other blood relatives and help you identify family members who are at risk. A genetic counselor can also coordinate tests for you and/or your family members and notify you if anything changes regarding your test results.
Do I need genetic counseling or genetic testing for FAP?
Since FAP is a hereditary syndrome, you should strongly consider genetic counseling. A genetic counselor can explain and educate about FAP and what it means for you and your family.
Importantly, your counselor will review cancer risks and screening recommendations for FAP and the benefits of doing increased screening starting at a younger age. Genetic testing, which can be done through a saliva or blood test, may be offered.
While genetic counselors help individuals consider all of their options and choices, the patient always has the final decision.
A genetic counselor can also explain how your personal health history may impact your other blood relatives and help you identify family members who are at risk. A genetic counselor can also coordinate tests for you and/or your family members and notify you if anything changes regarding your test results.
Explore these resources to locate a genetic counselor or a GI Cancer Genetics Clinic.
Explore these resources to locate a genetic counselor or a GI Cancer Genetics Clinic.
Are there varying degrees of FAP or are other genes involved?
Attenuated familial adenomatous polyposis (AFAP) is a less severe version of FAP. People with AFAP may experience it later than someone with FAP and may have 100 or fewer polyps. About 70% of people with AFAP will develop colorectal cancer if colon polyps are left untreated.
MUTYH-associated polyposis (MAP) is caused by mutations in the mutY homolog (MUTYH) gene. MAP, like AFAP and FAP, is a rare hereditary syndrome where people may develop 100 or fewer polyps, which likely may develop into colorectal cancer if left untreated. People with MAP may have an increased risk of developing other cancers as well.
While some of the features and cancer risks may be similar between AFAP and MAP, there are differences in screening recommendations and how the conditions are inherited. Because of this, genetic testing is extremely important to clarify the exact hereditary syndrome and what the risks are to other family members.
Are there varying degrees of FAP or are other genes involved?
Attenuated familial adenomatous polyposis (AFAP) is a less severe version of FAP. People with AFAP may experience it later than someone with FAP and may have 100 or fewer polyps. About 70% of people with AFAP will develop colorectal cancer if colon polyps are left untreated.
MUTYH-associated polyposis (MAP) is caused by mutations in the mutY homolog (MUTYH) gene. MAP, like AFAP and FAP, is a rare hereditary syndrome where people may develop 100 or fewer polyps, which likely may develop into colorectal cancer if left untreated. People with MAP may have an increased risk of developing other cancers as well.
While some of the features and cancer risks may be similar between AFAP and MAP, there are differences in screening recommendations and how the conditions are inherited. Because of this, genetic testing is extremely important to clarify the exact hereditary syndrome and what the risks are to other family members.
What should I do if I know or think I have FAP?
If someone has a family history of FAP, AFAP, or MAP remain proactive. Be sure to seek medical advice for a screening schedule based on family history or signs and symptoms. Also be sure to consider genetic testing.
What should I do if I know or think I have FAP?
If someone has a family history of FAP, AFAP, or MAP remain proactive. Be sure to seek medical advice for a screening schedule based on family history or signs and symptoms. Also be sure to consider genetic testing.
Medical Review
University of Colorado Cancer Center
Last Reviewed:
March 31, 2024
Medical Review
Institution University of Colorado Cancer Center
Last Reviewed: March 31, 2024