Biomarkers in colorectal cancer (CRC) give doctors important details about cancer’s risk, growth, and spread. They’re obtained through tumor biopsies and liquid biopsies.

Colorectal cancer (CRC) is one of the most common cancers worldwide. It affects millions of people and represents as many as 10% of all cancer diagnoses globally. Colon cancer and rectal cancer both fall under the category of CRC, which includes any cancer beginning in the colon or rectum of the large intestine.

Despite how common CRC is, mortality rates have improved in many countries due to advancements in screening and biomarker testing.

Biomarkers (short for biological markers) provide information about cancer. They’re a part of precision medicine and used to gain insight into cancer’s specific features. Biomarkers are measurable components, processes, or states of the body that act as indicators of health.

In CRC, biomarkers have many jobs. Some provide information about which treatments you should try or avoid, and others may provide insight as to how your tumor may behave in the future, or if cancer is still in your body after treatment ends. Biomarker tests can distinguish between acquired (somatic) genetic mutations and inherited ones (germline). They can also detect cancer-related protein levels, antigens, and changes in cell signaling pathways.

Common biomarkers in CRC include:

  • MSI-H/DMMR: This looks at microsatellites, short sections of repetitive DNA, and the function of DNA mismatch repair (MMR) genes.
  • Sidedness: This indicates which side of the intestine the CRC is found.
  • KRAS: This screens for mutations in the KRAS gene.
  • CEA: This measures levels of carcinoembryonic antigen.
  • ctDNA: This measures small fragments of circulating tumor DNA in the bloodstream.

Doctors use biopsies to perform biomarker testing in CRC. Biopsies collect fluid or tissue from the body for examination in a laboratory. Some biomarker tests in CRC require a tumor biopsy, while others can be performed through a liquid biopsy.

This guide can help you know what to expect if you need biomarker testing for CRC.

A note about colonoscopies

If an abnormality is found during a routine colonoscopy, a biopsy will likely be taken to verify whether the tissue is cancerous.

If an excisional biopsy or surgery is required after the initial colonoscopy, you will need to repeat the colonoscopy prep as described in the interactive section below.

Biomarker testing can be performed on this tissue.