Colon cancer develops when abnormal cells in the large intestine grow uncontrollably, often beginning as small growths (polyps) that can become cancerous over time. Some people inherit genes (traits passed down in families) that can increase their risk of developing colon cancer. Age, diet, and other health and lifestyle factors can also play a role.
When multiple family members develop colon cancer, it’s considered hereditary colon cancer. Parents who carry certain gene mutations (changes in genes that affect how cells grow) can pass them down to their children. These gene mutations make it more likely for abnormal cells to grow in the colon, increasing the risk of colon cancer. About 10% of all colon cancers are inherited and linked to specific hereditary conditions.
The two main genetic conditions that increase your risk are Lynch syndrome and familial adenomatous polyposis (FAP).
Lynch Syndrome
Lynch syndrome occurs when inherited gene changes disrupt the body’s ability to repair DNA (the material that stores genes), allowing abnormal cells to grow and divide more easily. People with Lynch syndrome have a lifetime risk of colon cancer of about 50%, depending on the type of gene involved.
Familial Polyposis (FAP)
FAP is less common but is associated with a high risk of colon cancer—nearly all people with FAP develop colon cancer by age 40. This happens because they grow hundreds or thousands of colon polyps, and these polyps almost always progress to cancer unless the colon is removed to prevent it.
While about 10% of colon cancer cases are tied to a clear inherited condition, up to 20% of people have a higher genetic risk of the disease. When multiple relatives have a history of colon cancer, it points to an inherited genetic risk even without a defined syndrome. If your grandparent, parent, or sibling has had colon cancer, your own risk may be higher.
In addition to genetics, lifestyle and health factors also affect your risk of developing colon cancer, including:
- Age (risk increases after age 50)
- A diet low in fiber and high in red or processed meat
- A sedentary lifestyle
- Alcohol or tobacco use
- Type 2 diabetes
- Inflammatory bowel disease (IBD)
- A history of radiation to the abdominal or pelvic area
Three ways to better understand your risk of colon cancer include:
- Family history: Ask your relatives whether anyone has had colon cancer or related cancers, such as uterine, ovarian, or stomach cancer. Gather information for at least three generations — including yourself and your siblings, your parents, your grandparents, and aunts and uncles. Ask what type of cancer they were diagnosed with and how old they were at the time. This information gives your doctor important clues about your inherited risk.
- Genetic counseling: If you have several relatives with colon cancer, or if family members were diagnosed before age 50, your doctor may recommend genetic counseling or earlier screening. Genetic counseling is usually done with a blood sample and can show whether you carry a known hereditary syndrome. A genetic counselor can explain the process, review the results, and discuss what they mean for you and your family.
- Cancer screenings: Even when no specific hereditary syndrome is identified, your doctor may recommend earlier or more frequent screening if colon cancer runs in your family. Colonoscopies are the most effective screening tool because they can both detect and remove precancerous polyps during the same procedure.
