Colon and Rectal Cancer
When colorectal cancer is diagnosed, several factors, such as the stage and location of the cancer, are used to determine the treatment plan. Today, oncologists also review genetic changes, called biomarkers, found in a patient before selecting the therapies likely to work best. Which genetic mutations lead to colon cancer, and which ones can be treated as part of a personalized treatment plan?
What are Cancer Biomarkers?
As our DNA changes over time, mutations in some genes lead to an overproduction of proteins or other molecules that enable cancer growth. Thanks to cancer research, some mutated genes can be targeted with recently developed categories of drugs.
Following a colorectal cancer diagnosis, your oncologist will likely perform biomarker testing, which you may also hear referred to as genomic testing or molecular testing. This testing is performed with a blood test or by testing some of the tissue removed during surgery or a biopsy. Keep in mind that some colorectal cancer patients will have genetic mutations that make them positive for specific biomarkers, and others won't.
The outcome of this analysis will provide helpful information about what type of treatment plans may offer the best outcomes.
Read our blog: How to Understand a Colon Pathology Report.
Here are some of the most common biomarkers related to colon cancer:
Types of Biomarker Tests for Colorectal Cancer
Biomarker testing doesn't look for inherited genetic mutations, only somatic mutations that develop in an individual over time. Talk to your oncologist about any family history, especially if a family member has precancerous polyps.
The two most common biomarker tests are genetic biomarker tests and protein biomarker tests.
Genetic Biomarker Tests
Genetic biomarker tests evaluate various genes associated with the growth of colorectal cancer, with more genes being tested as clinical research allows. Common genetic biomarkers considered in colorectal cancer treatment planning include BRAF, KRAS, NTRK, and HER2. As your oncologist gains more insights from the testing, adjustments might be made to the treatment plan.
Protein Biomarker Tests
Some biomarkers focus on finding proteins rather than specific gene mutations. For example, CEA is a protein that is elevated when the colon is inflamed. It is common for higher levels of this protein to be found in people diagnosed with colorectal cancer.
Additional Biomarker Tests for Colorectal Cancer
In addition to genetic and protein biomarkers, your doctor may also test sidedness and pathways.
- Sidedness is the side of the colon that has the tumor. Interestingly, right-sided tumors and left-sided tumors don't always share the same characteristics and may respond differently to treatment.
- Pathways or signaling pathways are biomarker types that evaluate the behavior of cancer cells. Common biomarker pathways that may be tested in colorectal cancer patients include the PD-L1 pathway, tumor mutational burden (TMB), and WNT pathway.
Which Colorectal Cancer Patients Should Undergo Biomarker Testing?
The biomarker tests will vary based on the patient’s stage and whether the cancer has recurred.
- Patients with any stage of colorectal cancer may be tested for an abnormality known as MSI-H/dMMR. Referred to as microsatellite stability, it measures the stability of a patient’s DNA. The number of microsatellite repeats in healthy cells is compared to the number of repeats in cancer cells. If all cells in the body have an equal number of microsatellite repeats, this is classified as microsatellite stable (MSS). Sometimes, cancer cells have too many or too few microsatellite repeats compared to healthy cells. When this occurs, the test will indicate that the patient has high microsatellite instability (MSI-H) biomarkers. Several approved immunotherapy drugs are available that can help slow the growth of cancer cells.
- CEA, a carcinoembryonic antigen, may be tested during follow-up visits for patients diagnosed with stage II, III, or IV colorectal cancer. This type of testing can help identify if cancer has recurred and gain other information about the tumor, which may prove helpful for treatment.
- Patients diagnosed with metastatic (stage IV) colorectal cancer may get tested for genetic alterations such as BRAF, KRAS, NRAS, NTRK, and HER2. Several targeted therapy drugs are available that can slow the growth of cancer when one or more of these biomarkers are present.
If you have already had surgery, ask your oncologist if biomarker testing was performed. If not, could it be done now? There may be information available that would alter the direction of your treatment plan. Knowing if biomarkers exist provides helpful information for your oncologist to develop the right colorectal cancer treatment plan for you.
Creating a Customized Treatment Plan with Biomarker Testing Results
As more research is conducted, more treatment options become available, allowing clinicians to take an even more customized approach to patient care. Treating cancer based on genes or mutations is referred to as precision medicine or personalized medicine because it considers specific characteristics of the patient's DNA.
Learning which biomarkers are present can help identify which targeted therapies may slow or destroy cancer cells. Many targeted therapies are available, targeting cancer cells specifically while avoiding nearby healthy cells. Because each patient is unique, what works for one person will be different than what is recommended for someone with other biomarkers or no biomarkers. After a complete review of your biomarker testing, your colorectal cancer doctor will determine your next steps.
The Path to Treatment Following a Colorectal Cancer Diagnosis
If you've been recently diagnosed with colorectal cancer or colorectal cancer has returned, you’re likely to have biomarker testing performed to investigate the best course of action.
At Willamette Valley Cancer Institute, we are committed to helping each of our patients by providing the most advanced and current colorectal cancer treatments available. We are dedicated to helping you throughout your journey. If you're located in the Willamette Valley or the Central Oregon Coast, find a colorectal cancer specialist at a location near you to discuss treatment and testing options or a second opinion on a treatment plan.
Related reading: What You Should Know About Treating Colorectal and GI Cancers
