While most colon cancers are NOT inherited, about 10 to 15% are caused by a single gene mutation passed through the family. Determining if a genetic susceptibility is contributing to a personal and/or family history of cancer may assist in medical decision making. This knowledge may also clarify the cancer risks of relatives, who may be reassured that they have not inherited a familial tendency and therefore do not require intensive screening.
When Should I Suspect a Colon Cancer May Be Hereditary?
When colon cancer is caused by a single gene mutation passed through the family you may see
- cancer diagnosed at an early age (e.g. under 50)
- Multiple family members (blood relatives) with colon cancer on the same side of the family
- constellation of colon cancer and uterine cancer in close family members or in an individual
- An individual with two or more primary cancers (colon and uterus)
- 3 or more cases of cancer of the colon, uterus, ovaries, small bowel, ureter or renal pelvis in close relatives on the same side of the family with one of the cancers diagnosed under age 50
- Rare tumor types (e.g. sebaceous carcinomas)
- personal or family history of ovarian, small bowel, ureter or renal pelvis cancer
- personal or family history of multiple precancerous growths, such as colon polyps
- sebaceous carcinoma or keratoacanthomas +/- family history of colon and/or uterine cancer
These features are only guidelines for assessing the risk for hereditary cancers. When these factors combine with a pattern in the family history that is recognizable to your physician or genetic counselor, it may indicate a hereditary risk for cancer. Colon breast and ovarian cancers are the most common types of cancer that have been linked to specific genes.
Is There a Test to Determine if Colon Cancer is Hereditary?
Genetic testing is available for hereditary colon cancer syndromes. The family history and cancer types in a family are used to determine the likelihood of a hereditary cancer syndrome and, if a syndrome is suspected, which gene(s) should be analyzed. The two most common hereditary colon cancer syndromes are Lynch syndrome (Hereditary Non-polyposis Colon Cancer or HNPCC) and Familial Adenomatous Polyposis (FAP). Genetic testing is available for both of these conditions.
Lynch syndrome (or HNPCC) is a condition in which the tendency to develop colon or rectal cancer is inherited. Non-polyposis means that colorectal cancer can occur when only a few polyps or no polyps are present. In Lynch syndrome, colon cancer occurs at an average age of 45, and tends to occur on the right side of the colon, also known as the ascending or proximal colon. Families with Lynch syndrome are also at increased risk to develop cancer of the uterus (40-60% lifetime risk), ovary (13% lifetime risk), stomach (13% lifetime risk), small intestine (~5% lifetime risk), brain (4% lifetime risk), ureter and kidney (4% lifetime risk), and biliary tract (2% lifetime risk).
A rare variant of Lynch syndrome includes sweat gland tumors (sebaceous adenomas, sebaceous epitheliomas or sebaceous carcinomas) and specific skin tumors (keratoacanthomas).
Familial Adenomatous Polyposis (FAP) is a hereditary cancer syndrome that is characterized by the development of hundreds to thousands of adenomatous colon polyps. Typically, polyps begin to develop in the late teens or early twenties, although the age of onset is variable. In addition to colon polyps, FAP has many other associated findings, including adenomatous polyps of the small bowel (small cancer risk), stomach polyps (which are benign), osteomas (benign bone tumors), cysts that develop on the legs, face, scalp, and arms, congenital hypertrophy of the retinal pigment epithelium (CHRPE, a red spot on the back of the retina that does not cause any problems) and desmoid tumors (benign fibrous tumors).
In addition to colon cancer, FAP can predispose to other cancers which include (the numbers in the parentheses are the lifetime risk of developing that specific cancer): duodenal or peri-ampullary (small bowel) (5-10%), pancreas (2%), thyroid (2%), stomach (<1%), and brain (<1%). If these cancers develop, it is typically later in life and with appropriate screening, most of these cancers can be detected at early, treatable stages.
Attenuated FAP is a variant of FAP that is characterized by the presence of fewer colonic polyps (less than 100) and a later onset of colon cancer than seen in classical FAP. Upper gastrointestinal polyps and cancer as well as other extracolonic features may be seen in individuals with attenuated FAP.
It is generally most informative if a relative who has had cancer is tested first, to determine if an identifiable gene mutation exists in the family. If a mutation is identified in an affected relative, at-risk family members may elect to be tested for the familial mutation; those testing positive have a significantly increased risk of developing cancer, while those relatives testing negative may be told that they have the general population risk of developing cancer.
What Should I Do Now?
Please use this section as background education. It is not a substitute for a clinical visit to our Center or discussion of a possible hereditary condition with your physician.
Take the next 10 to 20 minutes to fill out the online MyGenerations
for an initial evaluation of your risk of colon cancer.
Make an appointment with your physician to discuss your risk of cancer.
Make an appointment with the Center for Medical Genetics by calling 847.570.1029.
E-mail this page to a friend or loved one that may be at risk.