Family history of colorectal cancer or adenomatous polyps
Most colorectal cancers occur in people without a family history of colorectal cancer. Still, as
many as 1 in 5 people who develop colorectal cancer have other family members who have
been affected by this disease.
People with a history of colorectal cancer in one or more first-degree relatives (parents,
siblings, or children) are at increased risk. The risk is about doubled in those with only one
affected first-degree relative. It is even higher if that relative was diagnosed with cancer
when they were younger than 45, or if more than one first-degree relative is affected.
The reasons for the increased risk are not clear in all cases. Cancers can "run in the family"
because of inherited genes, shared environmental factors, or some combination of these.
Having family members who have had adenomatous polyps is also linked to a higher risk of
colon cancer. (Adenomatous polyps are the kind of polyps that can become cancerous.)
If you have a family history of adenomatous polyps or colorectal cancer, you should talk with
your doctor about the possible need to begin screening before age 50. If you have had
adenomatous polyps or colorectal cancer, it's important to tell your close relatives so that
they can pass along that information to their doctors and start screening at the right age.