The Role of Genetics
Genes are inherited from each parent. They determine various physical features and may predispose people to certain diseases. All cancers, but especially colon and rectal cancers, commonly referred to as colorectal cancer (CRC), have hereditary factors that potentially increase one’s risk. Genes are the underlying reason why many diseases such as CRC affect some families more often. For this reason, it is important to provide physicians with a detailed family history of cancer.
Colorectal Cancer Classifications
There are three broad classifications of CRC, two of which have a genetic component. The data below show the respective percentages for each type.
- Sporadic Colorectal Cancer: 50% to 60%.
- Familial Colorectal Cancer: 30% to 40%.
- Hereditary Colorectal Cancers: 4% to 6%.
Sporadic Colorectal Cancer
Sporadic colorectal cancer is the most common type, with 90% of people diagnosed at age 50 or older. It is not directly related to genetics or a family history. About 1 in 20 Americans develop this type of CRC. When a person is the first family member to be diagnosed with CRC, they should inform close relatives. People with a family history are advised to receive screenings at a younger age.
Familial Colorectal Cancer
Some families are predisposed to CRC. If a family has more than one relative with CRC, especially if it occurred before age 50, there is reason for concern. The risk for family members doubles when a first degree relative (parent, sibling or child) has it.
People with a close relative with CRC or colorectal polyps should receive their first screening at age 40, or 10 years before the youngest age at which the relative was diagnosed. These screenings should be done every five years, even if the test was normal.
Hereditary Colorectal Cancers
Hereditary colorectal cancers are associated with a specific inherited genetic abnormality. As genetic researchers continue to define certain syndromes, more genes that predispose one to CRC will likely be identified. Currently, some of the syndromes include:
- Hereditary Non-Polyposis Colon Cancer, Lynch Syndrome (HNPCC).
- Familial Adenomatous Polyposis (FAP).
- Attenuated Familial Adenomatous Polyposis (AFAP).
- APCI 1307K.
- Peutz-Jehger’s Syndrome.
- MYH Associated Polyposis (MAP).
- Juvenile Polyposis.
- Hereditary Polyposis.
Importance of Family Medical History
Family history information enables your colon and rectal surgeon to assess your risk of CRC and formulate the best plan for prevention and treatment. It is important to share the following:
- A’list of all family members diagnosed with colorectal polyps or cancer, with estimated age(s) at time of diagnosis.
- Family history of breast, ovarian or uterine cancer.
Additional patient evaluations can help detect and identify family cancer syndromes. These may include genetic counseling, formal genetic testing, colonoscopy, regular follow-up exams, and possible referral to other medical specialists.