As many as 150,000 cases of colorectal cancer are diagnosed each year. The majority of these cancers are sporadic , or not caused by inherited risk factors. However, up to ten percent of these cases are inherited, meaning they are caused by single genes that are passed on in families. Adenomatous polyposis syndromes are inherited colorectal cancer syndromes that are associated with multiple precancerous (adenomatous) polyps in the colon. There are three adenomatous polyposis syndromes: Familial adenomatous polyposis (FAP) and attenuated FAP (AFAP) are caused by an inherited mutation in the adenomatous polyposis coli (APC) gene. MYH -associated polyposis (MAP) is caused by inherited mutations in the MYH gene.
In FAP, hundreds to thousands of adenomatous polyps develop throughout the colon. These polyps usually begin to form around age 16. Unless removed, these polyps almost always develop into cancer. Additional features of FAP are desmoid tumors, osteomas, dental abnormalities and CHRPE (retinal pigmentation).
Attenuated FAP (AFAP) is a less severe variation of FAP. If a person has new polyps at every exam, or between 10 and 99 over several years, he or she may be diagnosed with AFAP. AFAP does not usually develop as early as FAP, but it carries a similarly high risk of cancer.
Individuals diagnosed with FAP or AFAP are not only at risk for colorectal cancer but may also have an increased risk over the general population for duodenal, gastric, pancreatic, hepatobiliary, thyroid and brain cancer. Colorectal cancer is the main condition seen in FAP and AFAP but these other cancers may also occur.
MYH -associated polyposis (MAP) may cause a large number of polyps in the colon, similar to FAP. However, it also may present with fewer colon polyps, as in AFAP. Due to the multiple colon polyps seen in MAP, the colorectal cancer risk is likely increased for these patients. At this time, it is unknown whether MAP is associated with other types of cancer.
If you feel you are at risk for any of the adenomatous polyposis syndromes, talk to your doctor about intensive screening, genetic testing and new drugs. These methods have substantially lowered the number of cases of colorectal cancer in certain families. Effective risk-reducing options are available to those patients who are at increased risk for cancer due to adenomatous polyposis syndromes.
* Cancer risks for MAP are currently unknown, although the association with multiple polyps is thought to increase the risk of CRC significantly.
Some individuals with adenomatous polyposis syndromes will have a family history of colorectal polyps and cancer, perhaps in their parents, grandparents, aunts, uncles, or siblings. However, it is important to remember that a significant number of patients with adenomatous polyposis syndromes will have no family history of colorectal polyps or cancer. Thus, even a single person in the family with multiple colon polyps is suspicious for inherited colorectal cancer.
What do we mean by inherited colorectal cancer? Genes like APC and MYH normally work to prevent certain types of cancer. But, in some cases, we can have a mutation in these genes. This mutation could have been inherited from our parents or it might have occurred early in our development. Either way, this mutation interferes with the normal activity of the gene, making us more susceptible to colorectal polyps and cancer.
If a person has mutations in the APC or MYH genes, their parents, children, brothers and sisters may also have the same mutation(s). Genetic testing is the only way to accurately identify individuals who carry mutations in these genes. If genetic testing leads to a diagnosis of an adenomatous polyposis syndrome in an individual, it is very important for them to share their test results with family members.
» Risk Reduction: Adenomatous Polyposis Syndromes
A genetic test for adenomatous polyposis
syndromes
