Colorectal Cancer Biomarkers

A Game-Changer for Treatment Options

If you’ve been diagnosed with colorectal cancer, you need to know about biomarkers and biomarker testing. It’s game-changing information and can significantly impact the decisions being made about you and your treatment plan. 

According to the NCCN Guidelines for Patients, “Biomarkers are specific features of cancer cells. Biomarkers can include proteins made in response to the cancer and changes (mutations) in the DNA of the cancer cells.”

A broad definition often comes with biomarkers, but it’s anything that can be used as an indicator of a disease.

Inside cancer tumors lie a variety of different markers, and tumor testing helps you and your doctor learn what’s inside your tumor and how to approach your treatment plan. Biomarkers allow your doctors to measure what’s objective and true about your cancer.

Your colon or rectal tumor might not respond to the same treatment that other colorectal cancer patients receive, depending on the biomarkers in your tumor.

What Is Biomarker Testing?

Biomarker testing may be referred to as tumor, molecular, mutation, somatic, or genomic testing. The actual test is most often performed on a small amount of tissue obtained from a tumor during a biopsy or surgery. If that’s not possible to collect, a blood sample may also be used.

The tissue or blood sample is sent to a specialized lab for testing and analysis. The lab will provide a report to your doctor based on its findings. Once your doctor receives your report, they should discuss it with you and explain how each finding can impact your treatment plan.

Not all colorectal cancers are the same. Your biomarker testing report will be specialized to you and your tumor, which should lead to personalized treatment planning.

Your Guide in the Fight

Download this FREE resource for stage III and stage IV colorectal cancer patients and their loved ones.

Who Needs Biomarker Testing?

All colorectal cancer patients need biomarker testing; however, not all patients need the same biomarker tests.

Here is who needs biomarker testing based on the 2022 NCCN Guidelines.

Depending on the type of biomarker test you receive, additional biomarkers may be found. Ideally, you will undergo these biomarker tests before beginning treatment.

Stage 0 & Stage IYour tumor needs to be tested for MSI-H/dMMR.
You need your CEA checked.
If your stage I cancer recurs, you need to be tested for biomarkers for metastatic disease.
Stage IIYour tumor needs to be tested for MSI-H/dMMR.
You need your CEA checked.
Ask your doctor if there is a role for ctDNA testing.
If your stage II cancer recurs, you need to be tested for biomarkers for metastatic disease.
Stage IIIYour tumor needs to be tested for MSI-H/dMMR.
You need your CEA checked.
Ask your doctor if there is a role for ctDNA testing.
If your stage III cancer recurs, you need to be tested for biomarkers for metastatic disease.
Stage IV / Metastatic DiseaseYour tumor needs to be tested for MSI-H/dMMR.
You need to know which side your tumor formed (Right or Left).
You need your CEA checked.
Ask your doctor if there is a role for ctDNA testing.
Your tumor needs to be tested for genetic alterations, including KRAS, NRAS, and BRAF mutations, HER2 amplification, and NTRK fusions.
Biomarker testing for metastatic colorectal cancer

Metastatic colorectal cancer is cancer that has spread beyond its original location in the colon or rectum and formed one or more tumors in other areas of the body, like the liver and/or lungs. Treatment possibilities for patients have been greatly extended due to biomarker testing, and especially for metastatic colorectal cancer patients.

If you’re a metastatic patient, it’s critical that you undergo biomarker testing, ideally before starting treatment, so you can know if you are likely to respond to available targeted therapies.

What Do Your Biomarkers Mean?

Some biomarkers tell what kind of cancer you have (diagnostic). Some are used to learn about the estimated course of cancer if it goes without treatment by determining cell functioning (prognostic), or if your tumor will respond well or poorly to certain treatments (predictive).

Biomarkers can give insights to dosing decisions (pharmacodynamic), and they can also indicate if cancer is in your body once treatment ends (recurrence).

Here are the most common and studied biomarkers in colorectal cancer patients that may impact your treatment plan.

How Is Biomarker Testing Done?

There are many types of biomarker tests that can be run on your tumor and/or blood. A gene includes multiple components, both protein-coding (exonic) and non-protein coding (intronic). The following tests may be run on your genes:

You and your doctor should decide on the type of biomarker test performed based on your unique and specific needs.

Biopsy Types

Biomarker testing is typically done by either tumor biopsy or liquid biopsy.

Tumor Biopsy

A sample of cells or tissues from the tumor to be examined by a pathology lab. There are incisional biopsies, where only a sample of tissue is removed; and excisional biopsies, where the entire tumor is removed.

Liquid Biopsy

A sample of blood that is analyzed for DNA fragments released from tumor cells or tumor cells in the blood. Pathology labs are looking for circulating tumor DNA (ctDNA) and/or circulating tumor cells (CTCs).

There are currently two liquid biopsy tests approved by the Food and Drug Administration (FDA) for biomarker testing: Guardant360 CDx and FoundationOne Liquid CDx.


I’ve seen the terms “somatic testing” and “germline testing.” What’s the difference and what does it have to do with biomarkers? 

Somatic testing looks only for changes inside the tumor, not changes happening inside your normal DNA. Somatic testing is what’s most closely associated with biomarker/tumor testing. Germline testing is genetic testing looking at mutations inherited from your biological parents and if there are changes in your DNA that predisposed you to cancer.

What if my doctor doesn’t recommend a biomarker test I know I need. (For example, if I have metastatic disease and I know I need HER2 evaluated).

First of all: Way to be an informed patient! Knowledge is power! Not all physicians are up to date on biomarkers and biomarker tests that need to be run. Make sure you take reliable information to your physician and ask them to check with NCCN guidelines for biomarker testing. It’s also never too late to get a second opinion if your physician won’t listen to you and take your questions and/or requests seriously. Your current treatment plan, previous biomarker testing reports, and insurance coverage should also be taken into consideration.

What will my results look like? Will I get to see them?

Your test results for gene testing for example, will show whether your tumor has a mutation (a genetic change – positive test results) or if it is wild-type (no genetic change – negative test results – no mutation detected). Your doctor should review your test results with you and discuss how they will affect your treatment decisions. If your doctor does not bring this up, ASK. You should receive a copy of your biomarker test results, and if you did not get a copy, make sure to ask. You own your records and have a right to them.

Is it possible to have both KRAS and BRAF mutations?

The most common mutations in the KRAS and BRAF genes do not normally occur together. It would thus be extremely rare. If your tumor has a BRAF V600E mutation, it will most likely not be KRAS mutant, and vice versa. Non-V600 BRAF mutations commonly co-occur with KRAS/NRAS mutations, particularly BRAF D594 mutations which are second most common after BRAF V600E mutations.

Why do I need biomarker testing before I start treatment?

If you begin receiving a treatment before knowing your tumor type, this may exclude you from future treatment options, including some clinical trials. Biomarker testing can also give insight as to whether or not you will respond to certain treatments based on the genetic changes inside your tumor. It’s worth taking the time to talk about tumor testing with your doctor before making treatment decisions, especially if you’re facing metastatic colorectal cancer.

What if I’ve received treatment already and I don’t know my biomarkers?

If you’ve already started treatment prior to tumor testing, it is recommended that you still receive the testing (it could affect your current treatment plan). The hospital where you had surgery most likely retained some of your tumor tissue. Contact your surgeon and connect them with your oncology team to learn more about how to get your sample sent to a pathology lab for testing. If your tumor tissue was not saved, ask your doctor about the best way to move forward with biomarker testing.

Will I need another biopsy to test my tumor?

Not usually. When you had surgery or a biopsy, some of your tumor tissue was removed and stored at the hospital. Your doctor can arrange for your tissue to be sent to a lab. The results will go to your doctor. The tissue sample tested can be from your original cancer in your colon or rectum, or from a metastatic tumor that has spread. If no tissue remains available, your doctor may suggest an additional biopsy to perform biomarker testing. If you’re getting biomarker testing with a liquid biopsy (blood), frequent blood draws will likely be required.

Why haven’t I heard about this before?

Your provider should be discussing biomarker testing with you, however not all providers use the word “biomarkers,” and not all providers realize it’s a term patient need to know. Your doctor may have been requesting some type of biomarker testing for you already, but did not mention or explain it. If you’re unsure if you’ve been tested for any biomarker, advocate for yourself and start the discussion. Our biomarker testing discussion guide is a great place to start.

What are the downsides of biomarker testing?

There are multiple biomarkers that have been scientifically shown to be meaningful in colorectal cancer. While more and more biomarkers are being studied, not all are shown to have clinical relevance or benefit the patient’s treatment decision-making. While knowledge is power and biomarkers can give you a wealth of information regarding your cancer and prognosis, you need to mentally and emotionally prepare yourself for biomarker testing, as some test results will show poorer prognosis and lead to a limited number of treatment options.

I’ve had genetic testing. Does this mean I’ve had biomarker testing?

Genetic testing is a type of biomarker testing, but it does not ensure that you have received all the biomarker tests necessary to make an informed treatment decision. Every colorectal cancer patient should have some type of screening for inherited cancer that’s looking for what’s been inherited from biological parents, what predisposes them to cancer. Genetic tests can be done by looking at someone’s blood to see what’s there and/or the consequence of a genetic alteration and look at the cancer itself. Tumor molecular profiling looks for genomic changes, to distinguish it from inherited genetic changes.

I’ve been told I have Lynch syndrome. Does this mean I’ve had biomarker testing?

This means that you have received MSI testing, which is one biomarker out of many. To learn if you have received and/or need testing for additional biomarkers, you will need to check with your doctor.

Will my insurance cover biomarker testing?

If you are participating in a clinical trial, the trial may cover the cost of biomarker testing. Private individual or employer-sponsored health insurers will usually cover biomarker tests when they are “medically necessary.” You and your doctor need to be on the same page, and it needs to be clear what biomarker tests are needed for your treatment plan. Biomarker testing is standard for all patients with metastatic colorectal cancer and should be done to guide treatment decisions if your tumor has spread beyond the colon or rectum.

Is there financial assistance for biomarker testing?

Some people may avoid testing due to perceived financial burden. Luckily, many labs offer patient assistance for out-of-pocket costs, and insurance companies may cover costs as well. Talk to a social worker and call your insurance provider to learn more.

Who makes the guidelines about biomarker testing?

In May 2017, four professional groups published evidence-based guidelines for biomarker testing for colorectal cancer. The Guideline, titled Molecular Biomarkers for the Evaluation of Colorectal Cancer Guideline from the American Society for Clinical Pathology, College of American Pathologists, Association for Molecular Pathology, and American Society of Clinical Oncology provides recommendations for mismatch repair status testing.

As of 2022, the National Comprehensive Cancer Network (NCCN) recommends microsatellite stability/instability (MSS/MSI) biomarker testing for all CRC patients, regardless of stage at diagnosis. Furthermore, they recommend KRAS, NRAS, BRAF, and HER2 biomarker testing for patients with stage IV, metastatic CRC.

There are several biomarkers without standardized recommendations. As research continues to evolve, guidelines and recommendations will also likely change to reflect the most relevant and meaningful research.

What if I need help facilitating my biomarker testing?

We strongly encourage you to talk with your doctor about ordering the tests. Without a physician referral, there is a potential that insurance won’t cover the testing, and it can be pricy. A doctor needs to be involved so you can take action about the results. If you need biomarker testing and your doctor refuses, we encourage you to seek a second opinion.

How do I have a conversation about biomarkers with my physician?

Sometimes you will need to advocate for yourself and start a conversation with your doctor about biomarker testing. To help guide your discussion, use this Biomarker Discussion Guide developed LUNGevity.

How often should I get biomarkers testing?

Biomarkers should be tested when you are first diagnosed. Testing for biomarkers at this time can help direct the best treatment for you. During treatment, you should continue to be tested for your CEAs and CA 19-9. These two biomarkers can be indicators of treatment effectiveness between scans. If you have a recurrence after being NED or if you have progression while you are on treatment, it may be a good time to be tested for your biomarkers – even if you have previously been tested. Because cancer involves mutations, biomarkers in your body may change over time. The repeated biomarker testing may reveal something new, indicating an effectiveness of a specific treatment that previously was not revealed. Make sure to ask about costs and coverage before you undergo testing.

Tell Your Story

Every day millions who are impacted by colorectal cancer are searching online looking for stories of people who’ve also faced this disease. When you share your experience, you let others know they are not alone.

Additional Resources

Medical Review

Rona Yaeger MD
Rona Yaeger, MD

Memorial Sloan Kettering Cancer Center

Last Reviewed: September 17, 2023
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