Health Information Library

By Mayo Clinic Staff

If someone in your family has been diagnosed with colon cancer, it's natural to wonder if it could be passed down to you or a loved one.

Colon cancer, also called colorectal cancer, develops when cells in the colon or rectum begin to grow in ways they should not. These changes can lead to the formation of clumps of cells on the lining of the colon, called polyps. Over time, some polyps can turn into cancer.

Colon cancer is one of the most common cancers and is a leading cause of cancer-related death in the United States.

Even though colon cancer is common, most cases are not inherited. Understanding how genetics and family history affect risk can help guide screening and prevention.

The terms "genetic" and "hereditary" are often used in the same way, but they do not mean exactly the same thing.

Genetic means a disease is related to changes in DNA. Hereditary or inherited means those DNA changes are passed from parents to children.

Most colorectal cancers involve genetic changes, but these changes are not inherited. Instead, they usually develop over time as cells continually grow and divide. About 75% of colorectal cancers occur without evidence of inherited disease.

Colon cancer is often grouped into three categories based on how it develops:

• Hereditary colon cancer is caused by inherited gene changes passed from parents to children. Certain conditions, such as Lynch syndrome or familial adenomatous polyposis, can significantly increase cancer risk and often occur at younger ages.
• Familial colon cancer occurs when cancer appears more often in a family, but no single inherited gene change is identified. This may be due to a combination of shared genes, environment and lifestyle factors.
• Sporadic colon cancer is the most common type. It develops from genetic changes that happen by chance and are not inherited.

This is why family history still matters, even when genetic testing does not show a known inherited condition. Understanding these differences can help guide decisions about screening, genetic testing and risk of colon cancer for family members.

Knowing your family history can help estimate your risk of colon cancer. Risk is generally higher when the affected family member is a first-degree relative, such as a parent, sibling or child. This risk may be about 2 to 3 times higher than average.

Risk may increase further when certain patterns are present, including:

• More than one relative with colorectal cancer.
• Early-onset colon cancer.
• One person with more than one type of cancer.
• Cancers linked to inherited conditions, such as uterine or ovarian cancer, occurring in the family.

These patterns may suggest a stronger genetic contribution to cancer risk.

Sharing your full family history with a healthcare professional can help guide decisions about screening and whether further evaluation may be helpful.

No. There are no specific symptoms that can confirm whether colon cancer is inherited.

Symptoms of colon cancer are generally the same whether the cancer is hereditary, familial or sporadic. These cancers develop in similar ways, so symptoms alone cannot determine the cause.

Yes. Most people who develop colon cancer do not have a family history of the disease. Instead, these cancers usually develop from genetic changes that occur by chance rather than inherited changes in genes, also called mutations.

Other factors also play a role, including lifestyle and environmental influences such as physical activity, diet and smoking.

Because colon cancer can develop without symptoms, screening is important even without a family history.

Several inherited conditions increase the risk of colon cancer, including:

• Lynch syndrome. Lynch syndrome is the most common hereditary colorectal cancer syndrome. It is caused by inherited mutations in genes that repair DNA, including MLH1, MSH2, MSH6 and PMS2. These gene changes allow DNA errors to build up, which increases cancer risk. Lynch syndrome also increases the risk of other cancers, including endometrial, ovarian and stomach cancers.
• Familial adenomatous polyposis. Familial adenomatous polyposis (FAP) is another inherited condition. FAP is caused by mutations in the APC gene. The condition leads to the development of many polyps in the colon. Without treatment, most people with FAP will develop colorectal cancer, often at a younger age.

Other inherited syndromes include MUTYH-associated polyposis, Peutz-Jeghers syndrome syndrome and juvenile polyposis syndrome. These conditions are less common but are important to identify because they can increase cancer risk. Because of this, they can affect when screening should begin and how often it is done. They also can help guide testing and risk assessment for family members.

Several genes are linked to hereditary colorectal cancer, including MLH1, MSH2, MSH6, PMS2, APC and MUTYH.

These genes help repair DNA or control how cells grow. When they do not function properly, cells can grow in uncontrolled ways and may become cancerous.

Genetic testing looks for inherited gene changes that increase cancer risk. Genetic testing is not needed for everyone. It is usually recommended when there are signs that colon cancer may run in a family.

A healthcare professional may recommend testing if:

• Colon cancer develops at a younger age.
• Multiple family members have had colorectal cancer.
• A known hereditary syndrome is present in the family.

Genetic testing usually uses a blood or saliva sample.

Genetic counseling is often recommended before testing to help explain results and next steps.

During a screening colonoscopy, cancer can be detected and sampled. Polyps also can be removed before they develop into cancer. Besides colonoscopy, other screening options may include at-home stool-based tests and blood tests.

Screening recommendations depend on individual risk. For people at average risk, screening begins at age 45. If someone in your family has been diagnosed with colon cancer, your healthcare professional may recommend starting screening at an earlier age.

Guidelines suggest starting at age 40 or 10 years before the age of the youngest member diagnosed in the family.

Colon cancers diagnosed at younger ages are more likely to be linked to inherited gene changes. A higher proportion of early-onset colorectal cancer is associated with inherited mutations compared with the proportion of colorectal cancer diagnosed later in life.

Even so, many early-onset cases still occur without a known inherited cause.

Even if you have a genetic risk, healthy habits may help lower your overall risk.

Helpful steps include:

• Staying physically active.
• Maintaining a healthy weight.
• Avoiding tobacco.
• Limiting alcohol.

These factors are linked to colorectal cancer risk and overall health.

Screening remains one of the most effective ways to prevent colorectal cancer because polyps can be found and removed early.

Colon cancer can be hereditary, but most cases are not caused by inherited gene mutations.

Family history still plays an important role in understanding risk. Sharing this information with a healthcare professional can help guide screening and genetic testing decisions.

Staying informed and keeping up with screening are important steps you can take to protect your health.