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Which biomarkers are tested in colon cancer? | CION Cancer Clinics
Every colon cancer should be tested for MMR or MSI. If the cancer has spread, RAS, BRAF and usually HER2 are added, because those results decide which drugs can work. This page explains what each biomarker is, when it is ordered, what the words on the report mean, and why your list may differ from someone else's. At CION Cancer Clinics, our team goes through your reports with you and plans the next test or treatment step.
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Medically reviewed by Dr. Naresh GunduConsultant Medical Oncologist · MBBS, DNB (Internal Medicine), DM (Medical Oncology, AIIMS) · last reviewed October 2026, next review due October 2027
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On this page
- Which biomarker tests are done in colon cancer?
- What each colon cancer biomarker tells your oncologist
- How does a biomarker test actually get done?
- What do the words on a biomarker report mean?
- Four things families assume about biomarker tests
- What this page cannot tell you
- Common questions about colon cancer biomarkers
The short answer
Which biomarker tests are done in colon cancer?
Everyone with colon cancer should have an MMR or MSI test on the tumour. If the cancer has spread, RAS (meaning both KRAS and NRAS), BRAF and usually HER2 are added, because those results decide which drugs can help. A biomarker is simply a feature of the tumour that a laboratory can measure and that changes a decision.
The test is done on tissue you have already given
Almost every biomarker test uses the biopsy taken at colonoscopy or the tumour removed at surgery. The laboratory keeps that tissue in a small wax block for years. A second biopsy is needed only when the first sample holds too few cancer cells to test.
The list depends on your stage
For cancer that is still inside the colon and nearby lymph nodes, the MMR result is often the only biomarker that changes anything. For cancer that has spread to the liver, lungs or lining of the abdomen, the full panel matters, because the drug added to chemotherapy is chosen from it. That is why two patients in the same ward can be offered different tests and both be right.
A biomarker test looks at the tumour, not at you. It is not the same as a family genetic test, although one result can lead to the other.The core panel
What each colon cancer biomarker tells your oncologist
Four tests make up the standard list. Each answers one practical question about treatment.
MMR or MSI
MMR (mismatch repair) proteins fix copying errors in DNA. When they are missing, the tumour is called MMR-deficient or MSI-high. This result can open the door to immunotherapy and can point to an inherited condition called Lynch syndrome.
Ordered for
- Every colon cancer, at any stage
- Stage 2 decisions on chemotherapy
RAS (KRAS and NRAS)
RAS genes act like an accelerator stuck on inside the cancer cell. If either gene is changed, drugs that block the EGFR signal, such as cetuximab and panitumumab, will not work.
Ordered for
- Cancer that has spread or come back
- Planning before liver or lung surgery
BRAF
A specific change called BRAF V600E marks a cancer that tends to behave more aggressively and has its own targeted combination. When MMR is deficient, BRAF also helps tell a chance change from Lynch syndrome.
Ordered for
- Cancer that has spread or come back
- MMR-deficient tumours, to sort out Lynch
HER2 and rarer targets
A small group of tumours carry extra copies of HER2, or rare changes such as NTRK fusions or KRAS G12C. Each has drugs aimed at it, mostly used after first-line treatment.
These are usually tested when RAS and BRAF come back normal, often on one broad gene panel.Not sure whether this applies to you?
Ask an oncologistFrom block to report
How does a biomarker test actually get done?
Your oncologist decides what to order
The choice follows your stage and the treatment questions that are still open. Ask for the list in writing, so you know which results to expect and which are not needed yet.
The pathologist picks the right piece
The pathologist (the doctor who reads tissue under a microscope) marks the part of the block richest in cancer cells. CION arranges this through accredited pathology and molecular laboratories.
The laboratory runs the tests
MMR is usually checked by staining the tissue for four proteins. RAS, BRAF and the rarer targets are read by DNA tests, increasingly a single next-generation sequencing panel that checks many genes at once.
The tumour board reads the results together
CION's tumour board puts the biomarkers beside your scans, your stage and the side of the colon the tumour started in. The treatment plan is chosen from all of it, never from one result alone.
On your report
What do the words on a biomarker report mean?
- pMMR or MSS
- Mismatch repair is working normally. This is what most colon cancers show, and it is not a bad result.
- dMMR or MSI-high
- Mismatch repair is broken. Immunotherapy may be an option, and Lynch syndrome needs to be considered.
- Wild-type
- No change found in that gene. "RAS wild-type" is the result that allows EGFR-blocking drugs.
- Mutated or mutant
- A change was found in that gene inside the tumour. It was not inherited and cannot be passed on.
- Amplified
- The tumour has extra copies of a gene, as happens with HER2.
- Insufficient sample
- Too few cancer cells to give a reliable answer. A repeat biopsy or a blood-based test may be suggested.
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Commonly believed
Four things families assume about biomarker tests
"A mutation in the report means our children will get it too."
RAS and BRAF changes arise inside the tumour during life. They are not in the rest of the body and cannot be inherited. Only an MMR-deficient result raises a family question, and a separate blood test answers it.
"The more genes tested, the better the treatment."
A test is useful only if its answer changes a decision. For early-stage cancer a large panel often adds cost without adding a choice. For spread disease, a broad panel can save tissue and time.
"A RAS mutation means no targeted therapy is possible."
It rules out EGFR-blocking drugs only. Bevacizumab, which works on the tumour's blood supply, is given whatever the RAS result.
"If the results are normal, the test was wasted."
A normal result is an answer. A RAS wild-type tumour gains an option, and a normal MMR result usually closes the Lynch question for the family.
Being straight with you
What this page cannot tell you
It cannot tell you which tests your own tumour needs. That depends on your stage, how much tissue is left in the block, and which treatment questions are still open. Your oncologist and the tumour board decide that, and they can explain why a test was left out.
It cannot read your report for you
The same gene name can carry very different weight depending on the exact change and the method used. If you have a report and are unsure what it means, bring it to a consultation rather than searching for the variant online.
Who this does not apply to
This page is about cancer of the colon. If your tumour is in the rectum, testing is similar but the treatment pathway differs, so start from the rectal cancer pages. If you are a relative wondering about your own risk, a tumour biomarker test is not your test; genetic testing after a diagnosis explains the family side.
Why RAS and BRAF are ordered before anything is started has its own page.Questions we are asked
Common questions about colon cancer biomarkers
Do I need a new biopsy for biomarker testing?
Usually not. The laboratory tests the tissue already stored from your colonoscopy biopsy or your operation. A new sample is needed only when too few cancer cells remain in the block, and then a blood-based test is sometimes used instead.
Why was only MMR tested and not RAS or BRAF?
For cancer that has not spread, RAS and BRAF rarely change the treatment, so many oncologists hold them back. They can still be run later on the same stored tissue if the cancer ever spreads or returns.
Is MMR testing the same as testing for Lynch syndrome?
No. MMR testing looks at the tumour and is a screen. If it shows a problem, further tumour tests and then a blood test on you decide whether Lynch syndrome is present. See why everyone gets MMR testing.
Can the test be done on a blood sample instead?
Sometimes. A liquid biopsy looks for tumour DNA shed into the blood. It is useful when tissue runs out, but it can miss changes when little tumour DNA is circulating, so tissue remains the standard first choice.
What is a next-generation sequencing panel?
A single DNA test that reads many genes at once, including RAS, BRAF, HER2 and rarer targets. It saves tissue and avoids running tests one by one. It costs more than a single-gene test, so it is chosen when the extra answers matter.
Do I need a test before chemotherapy itself?
Some centres check how your body breaks down certain drugs before starting them, such as the UGT1A1 test before irinotecan. That is a blood test on you, not the tumour. The UGT1A1 page explains it.
Is CEA a biomarker test?
CEA is a blood marker, not a tumour test. It is measured before treatment as a baseline and then used during follow-up to watch for change. It does not choose drugs and cannot diagnose colon cancer on its own.
Can CION arrange the testing?
Yes. CION's oncologists order the tests your stage calls for, and the work is done through accredited pathology and molecular laboratories. The tumour board then reviews the results with you. Call the helpline and someone will explain what is needed first.
Your Specialists
Meet CION's colon cancer specialists. Bring your colonoscopy, scan or biopsy report.
Our surgical and medical oncologists plan colon cancer care together: which operation, whether chemotherapy is needed, and the follow-up that comes after.
Medical Oncologist
Dr. C. Raghavendra Reddy
MBBS(Gold Medal), DNB(General Medicine), DM(Medical Oncology)(Gold Medal)
Medical Oncologist
Dr. Bharati Devi Gorantla
MBBS, MD(General Medicine), DM(Medical Oncology)(Adyar,Chennai), ECMO, MRCP SCE(UK)
Medical Oncologist
Dr. Owais Mohammed
MBBS, MD (General Medicine), DrNB (Medical Oncology), ECMO, MRCP SCE (Medical Oncology) (UK)
Medical Oncologist
Medical Oncologist
Surgical Oncologist
Dr. Muralidhar Muddusetty
MBBS (AIIMS), MS (Surgery) (AIIMS), DNB (Surgical Oncology), MRCS (Edinburgh)
Surgical Oncologist
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Sources
- American Cancer Society — Colorectal Cancer Targeted Therapy
- American Cancer Society — Testing for Colorectal Cancer
- NICE — Molecular testing strategies for Lynch syndrome in people with colorectal cancer
- ESMO — Colorectal Cancer: A Guide for Patients
This page is general information, not a prescription. Do not change or stop any treatment based on what you read here. If anything is worrying you, contact your own treating team — or call our helpline and we will help you reach the right specialist.
Keep reading
Related pages
Why RAS and BRAF testing comes before treatmentWhy the drug choice waits for these two resultsUniversal MMR and MSI testingThe one test every colon cancer should haveHER2 and rarer targets in colon cancerWhat happens when RAS and BRAF come back normalKRAS, BRAF and common mutationsHow the laboratory actually reads these genes
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Not sure which tests your tumour still needs?
Send us your biopsy or surgery report and we will tell you which biomarker results are already there and which, if any, are worth ordering. One helpline serves every CION centre.