Genetics and Family History in Colorectal Cancer

Most cases of colon cancer and rectal cancer are not considered hereditary, meaning you inherited a mutated gene from a family member.

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Is Colorectal Cancer Hereditary?

Most cases of colon cancer and rectal cancer are not considered hereditary, meaning you inherited a mutated gene from a family member. When it comes to colorectal cancer:

  • 60-70% of cases are sporadic 
  • 20-30% of cases are familial
  • 5-10% of cases are inherited/hereditary

Sporadic Colorectal Cancer

Sporadic colorectal cancer is what occurs in the majority of colorectal cancer cases. Sporadic colorectal cancers:

  • Form later in life (after age 50)
  • Don’t have a clear familial pattern
  • Don’t have an inherited gene mutation

Most cancer is sporadic, meaning you start with healthy genes and genetic mutations accumulate over time (typically due to age and environment). All individuals can benefit from learning their colorectal cancer risk.

Familial Colorectal Cancer

Family members may exhibit similar behaviors in terms of what they eat, their activity level, and their environmental exposures. This can lead to similar risks for developing colorectal cancer. When a family has a “cluster of cancers,” or multiple family members with cancer, it’s considered familial.

In addition, there may be multiple minor gene mutations that lead to a slight increased cancer risk, but these lower-risk gene mutations are currently unknown.

Family Members Impacted

It’s critical to know if anyone in your family has been diagnosed with cancer, what type, and at what age. Your risk is increased depending on how closely related you are and how old they were when they were diagnosed.

First-Degree Relatives

  • Parents (father or mother)
  • Siblings
  • Children

Second-Degree Relatives

  • Grandparents
  • Aunts & Uncles
  • Cousins
  • Nieces & Nephews
  • Grandchildren

If any of your biological relatives have been diagnosed with cancer before age 60, your risk may be doubled. Your risk may be even higher if a first-degree relative has cancer. It’s important to learn your family’s cancer history. For help with this, use our Family History Tool.

Family History Screening Guidelines

Screening recommendations for people with an inherited gene mutation are different from people who are at average risk of developing colorectal cancer. Ask your doctor and genetic counselor for screening recommendations based on your family history and genetic testing. 

You may need a colonoscopy and other cancer screenings sooner and more often, depending on your genetic testing results.

Learn more information about colorectal cancer screening options.

When Should You Get Screened for CRC?

If you have one first-degree relative diagnosed with colorectal cancer before age 60, or two first-degree relatives diagnosed at any age, you need to get screened at age 40 OR 10 years younger than the earliest diagnosis in your family, whichever comes first.

For example, if your mother was diagnosed with colorectal cancer at age 65, you need to get screened at age 40. If your mother was diagnosed at age 35, you need to get screened at age 25.

After your initial screening, you will likely need to have a colonoscopy every five years. If your family goes through genetic testing, your screening recommendations may change based on test results.

Hereditary Colorectal Cancer

Hereditary colon cancer and rectal cancer is caused by an inherited gene mutation. Knowing if your cancer is hereditary is extremely important because:

  • It can help you understand the underlying cause of your cancer.
  • It can tell you if you are at risk for developing other types of cancers.
  • It can tell you if other family members may be at risk of developing cancer.

Free Resource

Genetics Mini Magazine

This mini-magazine is designed to inform you about colorectal cancer that is passed down through families (called hereditary cancer) and genetic testing. Topics covered include:

Sporadic, familial and hereditary CRC
Testing: The steps and people involved
Emotional health and genetic testing
Types of hereditary CRC
Managing your risk of CRC
Increased risk/ familial risk management

How it Happens

Hereditary colorectal cancer occurs when a single gene mutation is passed down (inherited) through a family, leading to a potentially significant increased cancer risk among all family members. If you have a family history of colon or rectal cancer, it is important to learn if it is due to an inherited gene mutation so that each person in the family can follow recommended screening guidelines.

Types of Hereditary Colorectal Cancer

There are several common types of hereditary colorectal cancer syndromes. Here are the most common.

*This is not an all-inclusive list. For more information, download our Genetics Mini Magazine.

Lynch Syndrome (AKA Hereditary Nonpolyposis Colorectal Cancer)

Lynch Syndrome is the most common genetic syndrome associated with colorectal cancer. People with Lynch syndrome are at an increased risk for developing other cancer types and need more frequent screening and surveillance.

Here’s one family’s story about Lynch Syndrome.

What is Lynch Syndrome?

Learn more about Lynch syndrome.

Familial Adenomatous Polyposis (FAP) and Attenuated Familial Adenomatous Polyposis (AFAP)

The second-most common form of hereditary colorectal cancer is familial adenomatous polyposis (FAP). FAP occurs in one in 10,000 people and is detected by the growth of hundreds to thousands of polyps (adenomas) in the colon, often at an early age. The risk of developing colorectal cancer is 100% if left untreated. Attenuated familial adenomatous polyposis (AFAP) is a milder form of FAP, but still carries a higher risk for CRC than the average population. The gene that is associated with both FAP and AFAP is APC (adenomatous polyposis coli).

Learn more about FAP from our partners at ThinkGenetic.

MUTYH-Associated Polyposis (MAP)

Mutations in the MUTYH gene cause MAP. Parents and children of people with MAP are not generally affected by the disease because it has a recessive inheritance pattern.

Tell your doctor if you have a family member known to have MAP. It could mean a somewhat higher risk for colon cancer, and earlier, more frequent colonoscopies. 

Genetic Testing

The only way to know if you have hereditary colorectal cancer is through genetic testing. Anyone who meets the following criteria is a candidate for genetic testing.

  • Diagnosed with colon cancer or rectal cancer under age 50
  • Diagnosed with endometrial cancer under age 50
  • Multiple primary cancers or bilateral cancer (occurs in both paired organs—e.g., both breasts, kidneys, ovaries)
  • 3+ family members with a related cancer of Lynch syndrome
  • 2+ Lynch syndrome-associated cancers in a single family member
  • Has abnormal IHC for mismatch repair proteins in a tumor
  • Tumor that shows MSI
  • Family member has an identified gene mutation
  • 10+ polyps removed over the course of their lifetime, or a family member has had 10+ polyps

If you have concerns about your family history of cancer, speak with a doctor. If you have an incomplete biological family history, listen to our Taboo-ty podcast, “Unknown: What to do when you’re missing pieces of your family’s health history.”

Genetic counselors

Ideally, your doctor will refer you to a genetic counselor if there is a suspicion that you carry an inherited cancer mutation. But sometimes, you may need to advocate for yourself. Genetic counseling is an educational process in which your genetic counselor will explain in detail how families inherit cancer and how cancer grows. 

If you have a family history of colorectal cancer or if you or a family member has had numerous polyps, ask your doctor for a referral. You can also look for a genetic counselor online or by phone.

More Information

For more information about hereditary colorectal cancer, watch our Genetic Syndromes of Colorectal Cancer webinar.