Colorectal Cancer: Genetic Testing for Inherited Mutations

Why should people with colorectal cancer get genetic testing?

Up to 10% of people diagnosed with colorectal cancer have an inherited mutation that caused their cancer. 

• Genetic test results may affect your cancer treatment options, including allowing you access to newer therapies or to avoid therapies that are less likely to help you. 
• Genetic test results may help you and your relatives understand the risk for cancer and take action to stay healthy. 
• If you test positive for an inherited mutation, you may have an increased risk for other cancers.
• Your test may allow relatives to learn if they are at increased or average risk for cancer. 
• Expert guidelines outline cancer screening and prevention options for people who test positive for a mutation linked to colorectal cancer risk.   

Should everyone with colorectal cancer get genetic testing?

There are national guidelines that outline who should consider genetic counseling and testing for an inherited mutation linked to cancer. Speak with an expert about genetic testing for the following situations.

Guidelines for tumor testing followed by genetic testing

Experts recommend tumor testing all colorectal cancers to look for biomarkers known as "mismatch repair deficiency" (dMMR) or microsatellite instability-High (MSI-High) at the time of diagnosis. These two related abnormalities are commonly found in the cancers of people with Lynch syndrome.

• People with dMMR/MSI-High cancers are recommended to have genetic counseling and testing for Lynch syndrome. 
  • dMMR/MSI-High cancers can occur in people who do not have Lynch syndrome. Not all people with dMMR cancers will test positive for a Lynch syndrome mutation.
  • People with inherited mutations who develop colorectal cancer may have cancers that do not have these biomarkers. 
  • People with cancers that are not dMMR may still benefit from genetic counseling and testing. 

Guidelines for people with colorectal cancer and a history of polyps

Genetic counseling and testing for an inherited mutation is also recommended for people diagnosed with colorectal cancer who have any of the following personal history of polyps:

• 10 or more polyps of the adenomatous type.
• 2 or more polyps of the hamartomatous type.
• 5 or more polyps of the serrated type close to the rectum.

Guidelines for people with colorectal cancer and a personal or family history of cancer

Genetic counseling and testing for an inherited mutation is also recommended for people diagnosed with colorectal cancer who have any of the following:

• a blood relative with a known inherited mutation in a colorectal cancer gene.
• diagnosed before age 50.
• diagnosed with another Lynch syndrome related cancer including endometrial, ovarian, pancreatic, stomach or other Lynch syndrome-related cancer.
• a close relative with a Lynch syndrome-related cancer diagnosed under age 50.
• two or more relatives with a Lynch syndrome-related cancer diagnosed at any age.

Other colorectal cancer survivors who may benefit from genetic counseling and testing

Genetic counseling and testing is also recommended for anyone with the following family history of colorectal cancer:

• one or more 1st-degree relatives who has been diagnosed with colorectal cancer before age 50. 
• one or more 1st-degree relatives wo have been diagnosed with colorectal cancer and a second cancer related to Lynch syndrome (e.g., colon cancer). 
• two or more 1st- or 2nd- degree relatives who have been diagnosed with a cancer related to Lynch syndrome with at least one of the cancers diagnosed before age 50. 
• three or more 1st- or 2nd- degree relatives who have been diagnosed with a cancer related to Lynch syndrome at any age. 

Should relatives of people with colorectal cancer get genetic testing?

Genetic counseling and testing is recommended for anyone with the following family history of colorectal cancer:

• one or more 1st-degree relatives who has been diagnosed with colorectal cancer before age 50. 
• one or more 1st-degree relatives wo have been diagnosed with colorectal cancer and a second cancer related to Lynch syndrome (e.g., endometrial, ovarian, stomach, small intestine, urinary tract or other cancers). 
• two or more 1st- or 2nd- degree relatives who have been diagnosed with a cancer related to Lynch syndrome with at least one of the cancers diagnosed before age 50. 
• three or more 1st- or 2nd- degree relatives who have been diagnosed with a cancer related to Lynch syndrome at any age. 

Which genes are linked to colorectal cancer?

Mutations in the genes listed below are associated with an increased risk for colorectal cancer. The risks vary by gene. See our section with details for each gene to learn more. 

How do I get genetic testing for hereditary colorectal cancer?

Genetic testing is a type of blood or saliva test performed on blood, saliva or tissue. The sample is collected and sent to a genetic testing lab. A doctor or nurse with expertise in genetics or a genetic counselor can help you get genetic testing. You can read more about the process here.