What is attenuated familial adenomatous polyposis?

Attenuated familial adenomatous polyposis (AFAP) is a subtype of a condition known as familial adenomatous polyposis (FAP or classic FAP). An adenomatous polyp is a lump filled with the cells that line the inside of the colon and that make mucous. Normally these cells are in flat sheets, but in FAP and AFAP they build up into polyps inside the intestinal tract.

People with FAP or AFAP will have an increased number of adenomatous colon polyps during their lifetime and an increased risk of developing colorectal cancer. In AFAP, the total number of colon polyps is less than 100, with 30 being average. (In FAP, polyps are far more frequent.) Polyps in people with AFAP tend to develop later in life than in individuals with classic FAP, although polyps may develop as early as the late teens. Colorectal cancer develops later in AFAP as well, with the average age at diagnosis being around 50. Polyps and cancer of the stomach and small intestines are also seen in families with AFAP.

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. In addition, the risk for some of the other, noncancerous features associated with classic FAP has not been determined. For instance, there appears to be less chance with AFAP of having desmoid (noncancerous fibrous) tumors that can develop anywhere in the body or congenital hypertrophy of the retinal pigment epithelium (CHRPE), which is an eye condition. See Cancer.Net's Guide to Classic FAP for a full description of associated features.

What causes AFAP?

AFAP is a genetic condition. This means that the cancer risk can be passed from generation to generation in a family, but usually not all children of a person with AFAP will be affected. This is why people who are diagnosed with AFAP, and their family members, should talk with a genetics counselor or medical genetics specialist. The APC gene is linked to AFAP; APC stands for adenomatous polyposis coli. A mutation (alteration) in the APC gene gives a person an increased lifetime risk of developing multiple adenomatous colon polyps, colorectal cancer, and other cancers of the digestive tract. 

How is AFAP inherited?

Normally, every cell has two copies of each gene: one inherited from the mother and one inherited from the father. AFAP follows an autosomal dominant inheritance pattern, in which a mutation happens in only one 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. 

How common is AFAP?

Most colorectal cancer and colon polyps are sporadic (occurs by chance), not related to AFAP, classic FAP, or other inherited syndromes. The number of colorectal cancer cases and the number of people with multiple adenomatous colon polyps that are related to AFAP are unknown. It is possible that AFAP is under-diagnosed. 

How is AFAP diagnosed?

AFAP is suspected when a person has a history of more than 20, but less than 100, adenomatous colon polyps. People suspected of having AFAP can have a blood test to look for a mutation in the APC gene. If an APC gene mutation is found, a diagnosis of AFAP is confirmed. Other family members will be diagnosed with AFAP if they are tested and have the same gene mutation.

What are the estimated cancer risks associated with AFAP?

Estimated digestive tract cancer risks for classic FAP (unknown if risks are the same in AFAP)

What are the screening options for AFAP?

It is important to discuss with your doctor the following screening options, as each individual is different:

• Colonoscopy every two to three years, beginning at age 18
  
  
• Colectomy (the surgical removal of the entire colon) may be considered if polyps cannot be managed with regular colonoscopy because there are too many or in patients who cannot have colonoscopies on the recommended schedule above.

There is an increased risk of polyps of the upper digestive tract in AFAP, and regular screening should be considered as with classic FAP. The suggested screening for classic FAP is below.

• Upper endoscopy (EGD) every one to three years, beginning at age 25 or after polyps are detected
  
  
• X-ray or computed tomography (CT or CAT) scan of the small bowel if adenomas are found on the EGD or before a colectomy; repeat every one to three years depending on symptoms

It is unknown whether screening of the thyroid or screening for hepatoblastoma (a type of liver cancer) in young children is appropriate for families with AFAP as it is with classic FAP; see additional suggested screening for families with classic FAP. To learn more about what to expect during common diagnostic tests, read Cancer.Net: Tests and Procedures.

Screening options may change over time as new technologies are developed and more is learned about AFAP and classic FAP. It is important to talk with your doctor about appropriate screening tests.

Questions to ask the doctor

If you are concerned about your risk of colorectal cancer, talk with your doctor. Consider asking the following questions of your doctor:

• What is my risk of developing colorectal cancer?
  
  
• How many colon polyps have I had in total?
  
  
• What type of colon polyps have I had? (The two most common kinds are hyperplastic and adenomatous.)
  
  
• What can I do to reduce my risk of cancer?
  
  
• What are my options for cancer screening?

If you are concerned about your family history and think your family may have AFAP, 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?

Cancer.Net Guide to Colorectal Cancer

The Genetics of Colorectal Cancer

What to Expect When You Meet With a Genetic Counselor

Colon Cancer Alliance
www.ccalliance.org

Colorectal Cancer Coalition
www.fightcolorectalcancer.org

National Cancer Institute
www.cancer.gov

American Cancer Society
www.cancer.org

CancerCare
www.cancercare.org

To find a genetic counselor in your area, ask your doctor or visit the following websites:

National Society of Genetic Counselors
www.nsgc.org

National Cancer Institute: Cancer Genetics Services Directory
www.cancer.gov/search/geneticsservices