Most colorectal cancer is sporadic, which means it does not increase the risk of family members. Approximately 5-10% of all colorectal cancers are inherited, or caused by genetics.
Knowing if your cancer is inherited is extremely important because:
- It can help you understand the underlying cause of your cancer
- It can tell you if you are at risk for developing other types of cancers
- It can tell you if other family members may be at risk of developing cancer
Risks of Inheriting Colorectal Cancer
With inherited genetic abnormalities that increase the risk of colorectal cancer, there is generally a 50% chance that first-degree relatives (parents, siblings, children) inherit the same genetic abnormality and risk of developing cancer, however, other relatives could be at risk as well.
Knowing your family history can help you learn whether or not you should follow screening guidelines for higher risk individuals.
Genetic Counseling for Colorectal Cancer
Talk to your doctor about genetic counseling if you or a close family member has had:
- Cancer at a young age (under age 50)
- Multiple primary cancers or bilateral cancer (occurs in both paired organs—e.g., both breasts, kidneys, ovaries)
- Two or more close relatives with cancer, especially of the same type
- A relative who is a known carrier of an inherited cancer susceptibility
- Concern about your family history of cancer
Our genetics resources will help you dig up, track and understand your family’s cancer history.
If you or your biological relatives meet any of the above criteria, you may be at high risk for colorectal cancer and could benefit from a cancer genetics evaluation. Talk to your doctor or call our toll-free Resource Line for resources. Visit our resource library for resources regarding genetics and family history.
Genetic Syndromes Linked to CRC
There are several common genetic syndromes linked to colorectal cancer. This is not an all-inclusive list. View the National Cancer Institute’s information about additional genetic syndromes of colorectal cancer.
(aka hereditary nonpolyposis colorectal cancer)
Lynch Syndrome is a genetic syndrome that leads to an increased risk of colorectal cancer. Most of the time, the mutations that cause Lynch syndrome are located in the MLH1 or MSH2 genes, although there are others, and research continues to discover more. Only 3-5% of all colorectal cancer cases are linked to Lynch syndrome.
Signs of Lynch syndrome
Were you or a family member ever:
- Diagnosed with colon or rectal cancer before 50?
- Diagnosed with uterine/endometrial cancer before 50?
- Had 10 or more colon polyps over a lifetime?
- Two or more same-side family members diagnosed with colon, rectal or other Lynch-related cancers at any age (brain, breast, biliary tract, kidney, melanoma, ovarian, pancreas, small bowel, stomach, or uterine/endometrial)
The recommended age to start screening is age 20-25, or 10 years before the youngest case in the immediate family.
Learn more about Lynch syndrome from our partners at ThinkGenetic.
Familial Adenomatous Polyposis (FAP) and Attenuated Familial Adenomatous Polyposis (AFAP)
- Risk of developing colorectal cancer is about 100% if left untreated
- Average age at diagnosis: 39
- Average age of polyp formation: 16
People with FAP or AFAP will have an increased number of adenomatous colon polyps throughout their lifetime. The gene that is associated with both FAP and AFAP is APC (adenomatous polyposis coli).
The recommended age to start testing is between age 10-12.
Learn more about FAP from our partners at ThinkGenetic.
MYH-Associated Polyposis (MAP)
Mutations in the MYH gene (AKA: MUTYH gene), cause MAP. While the percentage of colorectal cancer that results from a MAP mutation is currently unknown, the risk of a person with MAP being diagnosed with colorectal cancer (and other cancers) is significantly increased.
To learn more about screening recommendations for people with a family history of CRC or for those with genetic syndromes linked to CRC, visit the American College of Gastroenterology and American Cancer Society.