Download Testing for Hereditary Cancers - FAP

Testing for Hereditary Cancers -
FAP -Familial Adenomatous Polyposis
FAP (familial adenomatous polyposis) is a hereditary colon cancer condition that affects about 1 in every 5,000 – 10,000 people. It accounts for about 1% of colon cancer cases. In families with FAP, people have an increased risk of developing large numbers of precancerous polyps (adenomatous polyps) throughout the colon. The large number of polyps makes the chance of colon cancer nearly 100%, unless the colon is removed. People with FAP may also develop benign (non-cancerous) polyps in the upper stomach and precancerous polyps in the lower stomach. They also have a slightly increased risk for cancer of the small intestine, thyroid, pancreas, and brain. A benign eye condition called congenital hypertrophy of the retinal pigment epithelium (CHRPE) is seen in people with FAP. CHRPEs are like freckles on the back of the eye and do not hurt a person’s eyesight. Gardner Syndrome
Gardner syndrome is a type of FAP. Besides the features described above, people with Gardner syndrome may also have:

benign skin changes such as fibrous (fibromas) or fatty (lipomas) tumors, as well as soft tissue tumors (desmoids) of the abdominal wall 
benign skin cysts, called epidermoid and sebaceous cysts 
benign bone abnormalities (osteomas) in the jaw, skull, fingers, toes
and long bones. 
dental problems such as extra, impacted, or teeth that have not come in While these rarely turn into cancer, they can cause both physical and cosmetic problems. Depending on where they occur, they may need to be removed. 1
AFAP- Attenuated FAP
AFAP is another type of FAP in which:

much fewer (10-100) polyps develop 
colon cancer is seen at a later age How are FAP, Gardner Syndrome and AFAP inherited?
Chromosomes are in every cell in our body. Each chromosome is made up of thousands of genes. Genes are the units of DNA that contain information that tell the cells how to work. When a gene changes or mutates, certain functions may be affected. FAP and its variant types are caused by mutations in the APC or MYH genes which control cell growth and division. Mutations in the APC gene are inherited in an “autosomal dominant” pattern:

Autosomal means that both men and women can inherit a gene mutation.

Dominant means that it takes only one gene mutation to have a problem. All people have two copies of the APC gene, one from each parent. If a person has a parent with an APC gene mutation, he or she has:

A 50 percent chance of inheriting the altered APC gene. 
A 50 percent chance of not inheriting the APC gene. The MYH gene is inherited in an “autosomal recessive” pattern:

Autosomal means that both men and women can inherit a gene mutation.

Recessive means that it takes two gene mutations to have a problem
– one from each parent.
People who have one MYH mutation and one normal MYH gene are called carriers. If two carriers have a child together, there is a:

25% chance that their child will inherit both MYH mutated genes, one from each parent, and have an increased risk for polyps and cancer. 
50% chance that the child would inherit only one mutation and would be a carrier 
25% chance that they would inherit both normal copies and would not be a carrier or have the FAP or AFAP.
2
If there is a mutation in the APC or MYH genes, they can no longer work correctly in the body and cause an increased risk of colorectal polyps and cancer. Testing for APC or MYH Gene Mutation
A blood or mouthwash sample is taken to test for APC and MYH mutations. If a mutation is found, other family members can be tested. Negative Result
Negative results mean an APC or MYH mutation is not found. It might mean that there is an APC or MYH gene mutation that cannot be found by current testing methods:

At least 10-35% of patients with a clinical diagnosis of FAP (over 100 adenomas in the colon) will not have a mutation detected in the APC gene. 
Even fewer AFAP families are found to have APC or MYH mutations. A negative test result could also mean that:

A different gene is responsible for the cancers or medical problems in the family. 
There is not a genetic link. If one member of a family has already been found to have an APC or MYH gene mutation, a negative result in any other family member means that person does not have FAP, Gardner syndrome or AFAP.
Positive Results
People with FAP have a 100% risk for colon cancer if they do not have their colon removed. The average age of diagnosis of colon cancer is between 35 and 43 years old.

75% FAP will develop polyps by age 20.

90% will have polyps by age 30.
FAP patients have a 10-12% lifetime risk for duodenal (part of the small intestine) cancer. People with FAP are also at increased risk for thyroid, pancreatic and brain cancer. The lifetime risk for each of these cancers is probably under 2%. Children with FAP have a 1-2% risk for hepatoblastoma – a form of liver cancer.
People with AFAP have fewer polyps, but the lifetime risk for cancer remains high.
3
Benefits of Testing
If a person is found to have a gene mutation, he or she should have careful screening to help find cancers at the earliest possible stage when they are most easily treated. Medication or surgery may be recommended to reduce the risk.
Learning the results can reduce the concern about risks of cancer and other problems. You and your doctor can determine how often to test for certain cancers. Risks of Testing
The genetic testing may be difficult emotionally. If mutation is found, it can possibly provide information about other family members who may have chosen not to be tested. The costs for the cancer screening and prevention options may or may not be covered by their health insurance. Understanding and making decisions about genetic testing can be a challenge. If you would like more information, call the Cancer Risk Program at 614-546-4330. Dev.11/07, Rev. 8/10, 1/14 \\mcehemcshare\Netit Patient Education$\Mount Carmel Handouts\Cancer\T esting - Hereditary Cancers\T esting for Hereditary Cancers - FAP - Familial Adenomatous Polyposis.doc
©Mount Carmel 2013
4