Colorectal cancer, commonly shortened to colon cancer, is one of the most common types of cancer. About 1 in 20 people will develop colon cancer during their life – someone with an average risk has roughly a 5% chance of developing colorectal cancer.
We’re commonly asked, “Is colon cancer hereditary?” It can be: A portion of colorectal cancer cases are caused by genetic mutations that are passed between parents and children. People who carry an inherited mutation that is associated with colon cancer have a higher risk of developing the disease.
Knowing if you have an inherited risk of colon cancer can give you a better understanding of your personal risks and screening needs. There are many services available that provide genetic screenings for colon cancer, including help from genetic counselors and community health research studies like myGenetics.
Below, we’ll help you understand the main causes of colorectal cancer and how to determine your personal risk of developing hereditary colorectal cancer.
There are three main causes of colorectal cancer
The causes of colorectal cancer can be broken down into three main categories: sporadic colon cancer, familial colon cancer and hereditary colon cancer.
Sporadic colon cancer
The most common cause is sporadic colon cancer – this affects between 50-60% of people diagnosed with colon cancer. This means that the cancer happens by chance. People who develop sporadic colorectal cancer are often the first in their families to be diagnosed with colon cancer.
Familial colorectal cancer
Familial colon cancer refers to a family where there are multiple people who have a history of colon cancer, but no known hereditary cause is found. It represents 20-40% of colon cancer cases. If more than one first-degree family member – a parent, sibling or child – has been diagnosed with colorectal cancer, your risk of developing the condition doubles.
People with a family history of colon cancer should get earlier and more frequent colon cancer screenings than someone with an average risk – usually every five years with an affected first-degree relative. Learn more about colon cancer screening guidelines.
Hereditary colon cancer
Hereditary colon cancer makes up the smallest portion of diagnosed colon cancer, accounting for 4-6% of colon cancer cases. This type of colon cancer is caused when parents pass on a genetic mutation that can increase risk for colorectal cancer in their children.
Although a family history of colorectal cancer may indicate that you’re at risk for carrying a genetic mutation that predisposes you to colon cancer, the only way to know for sure is to have a comprehensive hereditary cancer risk genetic test from a genetic counselor. There are several different types of genetic conditions that are linked to colon cancer, including but not limited Lynch syndrome and Familial Adenomatous Polyposis (FAP).
Colon cancer can run in families
Research shows that 1 in 3 people who develop colon cancer have a family member who also has the disease. It’s not always clear why colon cancer might run in a family. It may be caused by a combination of multiple low-risk genetic factors and environmental or lifestyle factors.
It also doesn’t mean you’ll develop colon cancer just because there are people in your family who have been diagnosed with the condition. However, a family history of colorectal cancer does increase your personal risk of colon cancer between 5% and 15%.
How to know if you have a family history of colon cancer
Having a family history of colorectal cancer means someone in your family has been diagnosed with the disease. Colon cancer is considered part of your family history if you have one immediate family member or at least two extended family members who’ve had the condition.
Those with an immediate family member like a parent, sibling or child are considered to be at a higher risk of developing colon cancer. Colon cancer screening guidelines recommend starting screening colonoscopies at 40 years old or 10 years earlier than when your first-degree family member was diagnosed – whichever comes first.
Colorectal cancer diagnoses in your extended family also affect your risk
Your extended family, sometimes called second-degree relatives, includes grandparents, uncles, aunts, cousins, nieces and nephews. If two or more of these relatives have been diagnosed with colon cancer, you may be at a higher risk of developing the disease.
While colon cancer screening guidelines don’t have specific recommendations for people with second-degree relatives with colon cancer, consider speaking with your primary care provider if you have any concerns. In some cases, genetic testing may be recommended in the setting of multiple affected extended relatives. Genetic counseling can help individuals decide if genetic testing is right for them.
Types of hereditary colon cancer
There isn’t one colorectal cancer gene that causes the disease – instead, there are several different genes that have been linked to colon cancer. Scientists are continuously researching the causes of colon cancer, and it’s possible that other genetic syndromes will be identified in the future.
The most common genetic syndromes that we know are linked to hereditary colon cancer are Lynch syndrome and familial adenomatous polyposis (FAP).
Lynch syndrome
Lynch syndrome (previously called hereditary non-polyposis colorectal cancer, or HNPCC), is the most common cause of hereditary colon cancer. Lynch syndrome results from an inherited mutation in one of five genes: MLH1, MSH2, MSH6, PMS2 or EPCAM. These genes help protect the body from certain cancers, but Lynch syndrome prevents them from working properly.
Lynch syndrome causes up to 3-5% of all colorectal cancer cases. It’s also linked to an increased risk of several other types of cancer, including colorectal, endometrial, gastric, ovarian, pancreatic, urothelial, brain, biliary tract and small intestine cancers. There are different screening intervals for each of these cancers, and risk-reducing surgeries for some of these cancers may also be recommended.
Lynch syndrome increases your risk of developing colon cancer
Someone with Lynch syndrome has a lifetime risk of developing colorectal cancer – the risk being between 15% and 61%. Lynch syndrome also increases the likelihood of developing colon cancer before age 50.
It’s important to remember that not everyone with Lynch syndrome will develop cancer. However, those with the disorder should follow different screening recommendations than people with an average risk.
Lynch syndrome can affect anyone
Lynch syndrome occurs in approximately 1 in 279 people in the United States. Most people with Lynch syndrome inherit the genetic mutation from their parents. It’s also possible for genetic mutations to randomly occur, though this is rare.
Familial adenomatous polyposis
Familial adenomatous polyposis (FAP) is caused by an inherited mutation in the APC gene and causes polyps to form in your colon and rectum. Polyps are growths of extra tissue that can turn cancerous if left untreated. People with FAP often develop colorectal cancer by age 40.
Those with FAP have almost a 100% risk of developing colon cancer if the polyps are not removed. It also increases the risk of developing several different types of cancer, including cancer of the small intestine, stomach cancer and pancreatic cancer. Less than 1% of colon cancer is caused by familial adenomatous polyposis.
If you have a family history of FAP or a personal history of 20 or more colon polyps, or if you are concerned about your personal risk of this genetic mutation, talk to your primary care provider.
Causes of familial adenomatous polyposis
In most cases, FAP occurs in people with a family history of the condition, and the inherited APC mutation is passed from parent to child. However, up to 30% of people with familial adenomatous polyposis have no family history of the condition.
Other types of hereditary colorectal cancer
Genetic researchers are working to understand all the genetic causes of hereditary colon cancer. Other less common causes of hereditary colorectal cancer include:
- Attenuated familial adenomatous polyposis (AFAP)
- Peutz-Jegher’s syndrome (PJS)
- MUTYH-associated polyposis (MAP)
- Juvenile polyposis syndrome (JPS)
- Hereditary polyposis
- Cowden syndrome
How to know if you have a risk of hereditary colon cancer
Everyone has a risk of colon cancer, but that risk is highest in people who have genetic mutations that cause hereditary colon cancer.
Genetic syndromes, like Lynch syndrome, often go undiagnosed. Many people don’t realize they have a risk of hereditary colon cancer or other genetic mutations until they’re diagnosed with colorectal cancer.
The only way to know if you’re at risk of developing hereditary colon cancer is to get colon cancer genetic testing. Genetic testing can cover all known colon cancer-related genes; however, there are still situations when genetic testing is unable to identify a causative mutation for those with a personal or family history of the disease.
Who should consider colon cancer genetic testing?
Genetic testing for colon cancer risk is available to anyone. However, the type of genetic testing you should consider is based on your personal and family history. Genetic screening for a subset of colon cancer genes related to Lynch syndrome is available through the myGenetics community health research study and is offered at no cost to you.
More comprehensive testing (often referred to as diagnostic or clinical testing) is also available and should be considered if:
- You have a personal history of colon cancer
- You have a personal history of 20+ colon polyps
- You have a personal history of a Lynch syndrome-related cancer before age 50
- Several members of your family have had cancers related to Lynch syndrome
- One of your family members has been diagnosed with Lynch syndrome
Genetic testing is the only way to diagnose hereditary colorectal cancer syndromes
The only way to know if you have a genetic mutation that causes colon cancer is to have genetic testing. Providing a small blood or saliva sample can help give you a picture of your personal health risk.
Understanding your risk of developing colorectal cancer can help you manage your long-term health. Those with a risk of hereditary colon cancer may benefit from lifestyle changes and specific colon cancer screening guidelines.
Genetic testing for hereditary colon cancer
If you think you would benefit from genetic testing for Lynch syndrome or other genetic conditions, you have two options: genetic counselors and genetic testing health studies. Both can provide colon cancer genetic testing services.
Genetic counselors
Genetic counselors can analyze your family medical history, coordinate clinical genetic testing and counsel you on your genetic health risks. They can offer robust screenings and talk with you about what your results mean for you and your family. If needed, genetic counselors can also guide you toward additional care you might need to manage your health risks.
In order to meet with a genetic counselor, you typically need a referral from another doctor. Insurance coverage for genetic counseling services vary depending on your insurance plan.
Genetic health testing studies
Genetic testing for Lynch syndrome and other genetic health conditions is sometimes available through DNA health studies and screening programs. Our large-scale community health research study, myGenetics, is one of the first of its kind in Minnesota. It’s a voluntary study available to all HealthPartners and Park Nicollet patients over the age of 18.
Genetic screening through myGenetics is offered at no cost to you and provides information about three specific hereditary conditions: Lynch syndrome, hereditary breast and ovarian cancer, and a hereditary form of high cholesterol called familial hypercholesterolemia. Information on regional ancestry and traits (like caffeine sensitivity) are also available to participants of the study.
Of note, myGenetics only screens for Lynch syndrome and not the less common genetic causes of colon cancer. If you have a personal or family history of colon cancer, you should also consider speaking with your primary care provider to discuss a referral to a genetic counselor. They can help determine if clinical genetic testing would be appropriate.
Learn more about genetic testing with myGenetics DNA health screening