Most people who develop colorectal cancer don’t have a family history. But as many as 1 in 3 people have other family members diagnosed with this type of cancer.

The American Cancer Society estimates 106,970 people will receive a diagnosis of colorectal cancer in 2023.

Cancer develops when gene mutations inside your cells cause them to replicate uncontrollably. Doctors usually don’t know why colorectal cancer develops, but a combination of your inherited genes and genetic mutations you acquire are both thought to play a role.

Most people who develop colorectal cancer don’t have a family history, but as many as 1 in 3 people have other family members who have had the disease.

Read on to learn more about what’s known about the genetics of colorectal cancer.

Researchers estimate between 12% and 35% of your risk of developing colorectal is attributed to genes inherited from your parents. The remainder comes from environmental factors.

Colorectal cancer rates vary between ethnicities, likely at least partially due to inherited genes. People of Eastern European Jewish descent have one of the highest rates of colorectal cancer.

Most people who have colorectal cancer don’t have a family history.

However, having relatives who had colorectal cancer seems to increase your risk too.

The risk seems to be highest if you have a first degree relative who had cancer when they were younger than 50, or if multiple people in your family had colorectal cancer. A first degree relative is somebody who shares half your DNA, such as a parent or sibling.

In a 2022 study from South Korea, researchers found that having a first degree relative with colorectal cancer was associated with a 1.5 times higher chance of developing colorectal cancer. Having a parent and sibling affected was associated with a 2.3 times higher risk.

Familial cancer syndromes

About 5% of people with a diagnosis of colorectal cancer have a familial cancer syndrome, according to the American Cancer Society.

A familial cancer syndrome is a predisposed risk of developing certain cancers due to genetic mutations passed through families. They often cause clusters of the same types of cancer among family members.

Syndromes associated with colorectal cancer include:

SyndromeLifetime risk of colorectal cancer
Lynch syndromeup to 80%
familial adenomatous polyposisnearly 100% if left untreated
Peutz-Jeghers syndromeabout 12%
MUTYH-associated polyposis80%–90%

What is HNPCC (Lynch syndrome)?

Lynch syndrome, also called hereditary non-polyposis colorectal cancer (HNPCC), makes up about 2% to 4% of colorectal cancers. It’s usually linked to mutations in genes that play a role in DNA repair, such as:

  • MLH1
  • MSH2
  • MSH6

Most people with gene mutations linked to Lynch syndrome will develop colorectal cancer. People with a uterus also have about a 60% chance of developing cancer in the lining of their uterus.

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Differences between familial adenomatous polyposis and colorectal cancer?

Familial adenomatous polyposis causes about 1% of colorectal cancers. This familial cancer syndrome is linked to changes in the APC gene. People with this condition often develop hundreds to thousands of polyps in their colons.

Almost everybody with familial adenomatous polyposis will develop cancer by age 40 if their colon isn’t removed.

People with familial adenomatous polyposis also have an increased risk of other cancers, including:

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The U.S. Preventive Services Task Force very strongly recommends colorectal cancer screening for adults ages 50 to 75. The task force also strongly recommends screening for people ages 45 to 49.

Doctors use five types of tests to screen for colorectal cancer:

If you have an increased risk of colorectal cancer, it’s a good idea to talk with your doctor about which type of screening is best for you.

If you’re between the ages of 76 and 85, it’s a good idea to have a conversation with your doctor to learn whether you may benefit from colorectal cancer screening.

Researchers have identified many gene mutations associated with the development of colorectal cancer. Knowing which mutations you have helps doctors determine how to best treat your cancer.

The most commonly mutated genes in people with colorectal cancer are:


Other risk factors for colorectal cancer include:

Genetic testing may be beneficial if you have a family history of colorectal cancer, especially if you have a parent or sibling with colorectal cancer.

Genetic testing can be performed with a sample of your:

  • blood
  • polyp
  • tumor

For people who haven’t yet received a diagnosis of Lynch syndrome, doctors often recommend testing if you meet the Amsterdam criteria:

  • You have at least three relatives with cancer linked to Lynch syndrome.
  • One relative is a first degree relative.
  • At least two generations in your family are affected.
  • At least one relative had cancer before age 50.

It’s important to get tested as soon as possible if you have a family history of familial adenomatous polyposis. The American Cancer Society recommends people with familial adenomatous polyposis to get screened with a colonoscopy as early as 10 to 15 years of age.

Most people who develop colorectal cancer don’t have a family history, but having a first degree family member with colorectal cancer increases your risk of developing it, too.

A small percentage of people with colorectal cancer have familial cancer syndromes. These syndromes often cause clusters of colorectal cancer within a family.