Guidelines for genetic testing in people diagnosed with colorectal cancer

Up to 10% of people diagnosed with colorectal cancer have an inherited mutation that caused their cancer. There are national guidelines that outline who should consider genetic counseling and testing for an inherited mutation linked to cancer.

Guidelines for testing in newly-diagnosed patients

Experts recommend that any person with colorectal cancer have tumor biomarker testing to look for an abnormality known as "mismatch repair deficiency" (dMMR or MMR-D) at the time of diagnosis. This abnormality is commonly found in the cancers of people with an inherited gene mutation linked to Lynch syndrome.

People with MMR-D cancers are recommended to also have genetic counseling and testing for an inherited mutation associated with Lynch syndrome. 

Not all people with MMR-D cancers will test positive for a Lynch syndrome mutation.

Additional guidelines for testing in any patient diagnosed with colorectal cancer

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

• Have 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
• Have 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 people who may benefit from genetic counseling and testing

You may benefit from additional genetic counseling and expanded genetic testing if you had genetic testing in the past, you tested negative, and the following applies to you:

• your situation matches any of the above, and
  • you had a test that only looked for one or a few genes, or 
  • you had genetic testing before 2014. Genetic testing has improved, and laboratories can now find gene mutations that may have previously been missed.

Colorectal cancer survivors and those in treatment should speak with a genetics expert to see if testing is right for them. 

Genetic testing for relatives of people who have been diagnosed with colorectal cancer

Genetic counseling and testing is also recommended for anyone with a first-degree or second-degree relative who has been diagnosed with colorectal cancer before age 50. 

See our sections Testing Guidelines by Cancer Type and Genetic Testing for People Who Have Never Been Diagnosed with Cancer for additional guideline information.