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What is attenuated familial adenomatous polyposis?
Attenuated familial adenomatous polyposis (AFAP) is a subtype of a condition known as familial adenomatous polyposis
(called FAP or classic FAP). 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.
An adenomatous polyp is a lump filled with the cells that make mucous
and line the inside of a person's colon. Normally these cells are in
flat sheets, but in FAP and AFAP they build up into polyps inside the
intestinal tract. 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 can develop later in people with 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. Risks for some
of the other, noncancerous features associated with classic FAP have not
been determined. For instance, people with AFAP appear to have a lesser
chance of developing desmoid tumors (noncancerous fibrous tumors that
can grow anywhere in the body) or congenital hypertrophy of the retinal
pigment epithelium (CHRPE, which is an eye condition), than people
diagnosed with FAP. Find out more about classic FAP.
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. The gene associated
with AFAP is APC; 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. People who are diagnosed with AFAP, and their family
members, should talk with a genetics counselor or medical genetics
specialist (a health professional with specialized training in medical
genetics).
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?
AFAP is uncommon and possibly under-diagnosed. 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.
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?
The cancer risks for AFAP are considered to be similar to the risks
associated with classic FAP, but the overall cancer risks may be lower.
As more information is learned about AFAP, more specific cancer risks
may emerge.
- Colorectal cancer: considered to be high, but less than 100% (if not treated)
Estimated digestive tract cancer risks for classic FAP. (It is
unknown if risks are the same in AFAP but screening is suggested due to
the similarities in both syndromes.)
- Small bowel (intestines): 4% to 12%
- Pancreatic cancer: 2%
- Stomach: 0.5%
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). This may be considered if polyps cannot be managed with regular colonoscopies because there are too many or if a patient 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 similar to
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.
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.
Learn more about what to expect when having common tests, procedures, and scans.
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?
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