Colorectal Cancer: Biomarker Testing
Testing for People with Colorectal Cancer
This section covers the following topics:
testing for treatment selection
tests look at samples of blood, tumor or other tissue for changes or abnormalities caused by cancer. These tests can give doctors clues about the cancer, including:
- how fast the cancer is growing
- which treatments are most likely to work
- whether or not the cancer is responding to treatment or growing
- whether or not the cancer has come back after remission
tests may be used to select treatments, and help patients avoid side effects from treatments that will not work for them. tests used to select a specific treatment are sometimes called "companion diagnostic tests." These tests may be done on tumor tissue or (in many cases) on blood. See our Testing section for more information.
After colorectal cancer tissue is removed by surgery or biopsy, all colorectal cancers should be tested for an abnormality known as (MSI), also known as "" ( or ).
MSI and MMR testing
Experts recommend testing all colorectal cancers for biomarkers known as “" and, or "" ( or ). These biomarkers measure how well the tumor can repair certain types of damage. The results have similar meaning.
- Microsatellite instablity results are reported as MSI-H ( high), MSI-L ( low) or MSS (microsatellite stable).
- Mismatch repair results are reported as or (mismatch repair deficient) or pMMR or MMR-P (mismatch repair proficient).
- and cancers are common in people with a gene mutation.
- People with advanced or MSI-high colorectal cancer may respond well to a type of known as an immune checkpoint inhibitor.
Other biomarkers for colorectal cancer treatment
- Experts recommend testing colorectal cancers for the following biomarkers to help guide treatment selection:
- Mutations in a gene known as RAS (KRAS and NRAS).
- A specific mutation in a gene known as BRAF.
- (also known as HER2/neu). Tumors that have this are known as . These tumors may respond well to a type of known as anti-HER2 therapy.
- Additional tests may be used in colorectal cancer:
- A known as an NTRK fusion is rare in colorectal cancer. People with advanced/metastatic colorectal cancer with an NTRK fusion may benefit from the Vitrakvi (larotrectinib).
- Additional tumor testing may help people learn if they are eligible for certain clinical trials.
Genetic testing for inherited mutations to guide treatment selection
About 10 percent of colorectal cancers are caused by an . Some genetic test results can help guide treatment decisions.
- People with are more likely to have MSI-H or cancers.
Visit this section for more information on who should consider genetic testing and the genes associated with hereditary colorectal cancer.
