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.
Hereditary Nonpolyposis Colorectal Cancer (Lynch Syndrome)
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.
Although 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:
- At least three members with a Lynch syndrome-related cancer
- At least two successive generations with this type of cancer
- Two family members with the disease are first-degree relatives (i.e. parents, brothers, sisters, or children) of another family member with a Lynch syndrome cancer
- At least one member affected at or before age 50
- FAP is excluded from the family member's diagnosis
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) Syndrome
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.
What Is the FAP Gene?
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%.
What’s the Difference Between FAP and HNPCC?
The two main differences between FAP and HNPCC are:
- Number of genes involved. In FAP, only one gene, APC, has a mutation. In HNPCC, several gene changes may be responsible for the condition.
- Presence of polyps. FAP is marked by the presence of more than 100 benign polyps. People with HNPCC have fewer polyps, but they can become cancerous more quickly than normal.
Other Forms of Inherited Polyposis Syndromes
Other very rare forms of inherited polyposis syndromes are linked with a higher risk of colorectal cancer. These include:
- Juvenile polyposis (JP). You may have five to 500 polyps, mostly in the colon and rectum. They usually happen before the age of 10. The stomach and small intestine may also be affected. People who have JP are also more likely to get bowel cancer.
- Peutz-Jeghers syndrome (PJS). People with PJS typically have dozens to thousands of benign polyps in the stomach and intestines, mostly in the small intestine. The growths can become malignant or can cause a blockage of the bowel.
Ashkenazi Jews and Colorectal Cancer
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 anJewish 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.
Gene Tests for Colorectal Cancer
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:
- You’ve had more than 10 colon polyps
- You’ve had colon polyps and other types of tumors
- You’re of Ashkenazi Jewish descent and your family has a history of colon cancer or polyps
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.
Colorectal Cancer Registries
A few medical centers across the country keep lists, or registries, of patients and their families with conditions tied to colorectal cancer like HNPCC, FAP, and Peutz-Jeghers syndrome. These registries collect and manage information about family history and biological samples.
The registries’ goals include:
Patient care. The first step to joining a cancer registry is to talk about it with your family and sign a consent form that allows registry workers to contact your relatives and get medical records from other hospitals. This way, they can build a family tree, called a pedigree, that tells the story of cancer in your family. It’s the key to sorting out who is at risk, how strong the risk is, and what needs to be done. Registry workers coordinate testing, appointments, and treatments. They may also offer advice about insurance concerns, payment problems, or any other issues. Any personal information that the registry gathers about you is confidential.
Education. You and your family need to be aware of how this condition will affect your lives. You can keep up with developments through booklets, newsletters, and articles from medical journals. Registries also take part in programs to educate doctors about the complexities of inherited colorectal cancer.
Research. You and your family may be asked to take part in research projects aimed at improving care for colorectal cancer patients and their families. Registries lead the way in this research because they have access to large numbers of people. Safeguards built into the research process protect you from harm. Registries and their workers can also share ideas and collaborate on studies with other registries around the world.
Colorectal cancer registries also:
- Encourage screening. Registry workers can build a trusting relationship with patients and their families so that honest feelings and fears may be discussed and dispelled. They can help patients understand the importance of screening for themselves and other family members.
- Serve as patient advocates. Registry workers have the best interests of you and your family in mind. In addition to medical problems, many patients and families need help with aspects of their lives such as insurance, employment, or social issues. For these things, you can rely on the registries as a resource.
Anyone with a strong family history of colorectal cancer (more than two close relatives with the disease) may join an inherited cancer registry.
Talk to your cancer team if you’re interested. They can help you find one that’s right for you.