Mar 15, 2022
Experts have found gene changes (also known as mutations or abnormalities) that cause colorectal cancer. A gene is a block of DNA that holds the genetic code, or instructions, for making proteins vital to our bodily functions.
The children of people who carry these genes have a 50% chance of getting them from their parents.
The two most common inherited colorectal cancer syndromes are hereditary nonpolyposis colorectal cancer (HNPCC) and familial adenomatous polyposis (FAP). These two account for less than 5% of all colorectal cancers.
HNPCC, also known as Lynch syndrome, is the most common form of hereditary colon cancer, accounting for about 3% of all colorectal cancer diagnoses each year. People with HNPCC often have at least three family members and two generations with colorectal cancer, and cancer develops before age 50.
lthough not everyone who inherits the HNPCC gene will get colorectal cancer, the risk is very high: about 80%. People with HNPCC also have a higher risk of other Lynch syndrome-related cancers, including brain, kidney, ovarian, uterine, bladder, pancreatic, small intestine, and stomach cancers.
Doctors can check the pattern of colorectal cancer in relatives in order to find out if the family has HNPCC. "HNPCC families" must show certain signs of a pattern of colon cancer across generations. These are called the Amsterdam Criteria and include:
Check with your doctor if you think this applies to your family. Colonoscopies are recommended in family members who are 10 years younger than the youngest family member who was diagnosed with cancer. You should also be screened for other Lynch syndrome-related cancers. For people with a diagnosis of Lynch syndrome, screening usually starts between ages 20 and 25.
Familial adenomatous polyposis (FAP) is a rare condition marked by the presence of hundreds or thousands of benign polyps, noncancerous growths in the large intestine and upper respiratory tract. It’s thought to happen in about 1% of all people diagnosed with colorectal cancer each year.
The polyps start early, with 95% of people with FAP getting them by age 35, and are often found in patients in their teens, with 50% having polyps by age 15. Without colon removal, there is almost a 100% chance that some of the polyps will become cancer, usually by age 40. Thyroid cancer is also linked with FAP.
Although most cases of FAP are inherited, nearly a third are the result of a spontaneous (newly occurring) gene change. For people who develop a new gene mutation, they might pass the FAP gene on to their children.
Genes are tiny segments of DNA that control how cells function, such as telling them when to divide and grow. One copy of each gene comes from your mother; the other comes from your father.
In 1991, researchers identified the gene called APC that is responsible for the condition. It can be found in 82% of patients with FAP. The lifetime risk of colon cancer in people who have this gene change is close to 100%.
The two main differences between FAP and HNPCC are:
Other very rare forms of inherited polyposis syndromes are linked with a higher risk of colorectal cancer. These include:
Jewish people who are Ashkenazi, or of Eastern European descent, are at increased risk for colorectal cancer. This is thought to be due to a variant of the APC gene that is found in 6% of this population. Ashkenazi Jews make up the majority of the Jewish population in the U.S.
If you suspect that you are at risk for Jewish people who are Ashkenazi, or of Eastern European descent, are at a higher risk for colorectal cancer. This is thought to be due to a variant of the APC gene that is found in 6% of this population. Ashkenazi Jews make up the majority of the Jewish population in the U.S. inherited form of colorectal cancer, talk to your doctor. There may be a genetic test that can be performed to confirm your suspicions.
Blood tests can find the gene changes that make some people more likely to get FAP or HNPCC.
You might want to consider genetic counseling and testing if:
If you test positive for these gene changes, your doctor will probably recommend that you get a colonoscopy every year. This is a test that checks your colon for cancer or polyps.
If you’ve already had colon cancer or polyps, your doctor may talk to you about a colectomy, which is surgery to remove your colon.
Your relatives might want to consider genetic counseling and testing, too.