Medical Oncologist
CION Cancer Clinics
HER2 and rarer targets in colon cancer: who is tested and why | CION Cancer Clinics
HER2 testing in colon cancer is mainly for people whose cancer has spread. Only a few tumours in every hundred make too much HER2, but when one does, drugs that block it can become an option. This page explains who is tested, how the test is done on tissue you have already given, and what HER2 and other rare targets can and cannot change. 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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The short answer
Does my colon cancer need a HER2 test?
Usually only if the cancer has spread. HER2 is a protein that sits on the surface of some cancer cells. When a tumour makes far too much of it, a group of drugs that block HER2 can help. In colon cancer this happens in only a few tumours in every hundred, so the test matters most when the cancer has reached the liver, lungs or elsewhere and your oncologist is planning more than one line of treatment.
Why it often travels with the RAS and BRAF tests
Extra HER2 turns up mostly in tumours where the RAS and BRAF genes are normal. So HER2 is usually checked alongside those genes, or straight after them, often on one gene panel. If you have not met RAS and BRAF yet, read why RAS and BRAF testing comes before treatment first.
What a HER2 test does not tell you
It does not tell you how far the cancer has spread or how long anyone will live. It is not a test for inherited risk either. That job belongs to the MMR or MSI test, which every colon tumour should have, as explained on universal MMR and MSI testing.
Will waiting for it delay treatment?
Rarely. HER2-blocking drugs are usually kept for later in the plan, so the first treatment can start while a slower panel is still running. Your oncologist will say if a result needs to be back before anything begins.
HER2 is a question about which drug, not about how serious the cancer is.Beyond RAS and BRAF
Which rarer targets might your oncologist look for?
Each of these is uncommon. Each one, if found, can open a treatment that would otherwise not be offered.
HER2 amplification
The tumour carries extra copies of the HER2 gene and makes too much of the protein. Drugs that block HER2, usually given in pairs, are then an option, most often after standard chemotherapy has been used.
More often found in
- Tumours with normal RAS and BRAF
- Cancers on the left side of the colon
KRAS G12C
One particular spelling change in the KRAS gene. Most RAS changes still have no matching drug, but this one does, given together with an antibody such as cetuximab. Access in India is limited and changes, so ask what is currently available.
Other KRAS changes still point away from cetuximab, exactly as before.NTRK, RET and ALK fusions
Two genes break and join together, creating a faulty switch. These are very rare in the colon, but the matching tablets work across many cancer types once the fusion is found.
More often found in
- MSI-high tumours
- Tumours with normal RAS and BRAF
- Right-sided cancers
POLE and a high mutation count
Some tumours carry a huge number of gene changes, sometimes because a repair gene called POLE is broken. These can respond to immunotherapy in a way most colon cancers do not.
This is separate from MSI-high status, which is the commoner reason immunotherapy is offered and is checked on every tumour.
Not sure whether this applies to you?
Ask an oncologistFrom sample to result
How is HER2 actually tested on your sample?
The tissue block is found
The test uses tumour already removed at biopsy or surgery, stored in a small wax block. No new procedure is needed if enough tissue is left. If you were diagnosed elsewhere, ask that laboratory to release the blocks and slides.
A stain scores the protein
A pathologist stains a thin slice and scores it as 0, 1+, 2+ or 3+. The rules for bowel tumours are stricter than the rules used for breast cancer, so the report should say which scoring system was followed.
A borderline score is checked again
A 2+ result is unclear. A second test, called ISH, counts the copies of the HER2 gene directly and settles whether the tumour is truly positive.
Or a gene panel reads many targets at once
Many oncologists now order one panel that looks for HER2, KRAS G12C and fusions together, which saves tissue. When tissue runs out, a blood test that reads tumour DNA can sometimes help, though a negative blood result does not rule a target out.
Side by side
What a HER2 result changes, and what it does not
HER2-positive
HER2-negative
HER2-blocking drugs join the list of later options
Standard chemotherapy and targeted drugs are planned as usual
Cetuximab-type drugs may work less well
RAS and BRAF results guide the choice of antibody
Usually does not change the first treatment
Other rare targets may still be worth a look
Says nothing about inherited risk
Says nothing about inherited risk
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Did you know
A tumour can carry a different set of gene changes after several lines of treatment. If a target was not found at diagnosis, your oncologist may sometimes repeat the panel later, on fresh tissue or on blood.
Being straight with you
What this page cannot tell you
It cannot tell you whether your tumour carries any of these targets. Only a test on your own tissue answers that. It also cannot tell you whether a matching drug is right for you, because that depends on what you have already received, how you are coping and what is available and affordable. At CION, the tumour board reviews every result before a plan is made, as described on the tumour board and who decides your treatment.
Who this does not apply to
If your cancer is stage one to three and has been removed, HER2 and these rarer targets usually do not change whether you need chemotherapy after surgery. Your stage, the lymph node count and the MMR result do that. If your tumour is in the rectum, the testing logic is similar but the rest of your care differs, so start at the rectal cancer hub.
When the evidence is thin
Some of these drugs were approved after studies in small groups, because the targets are rare. Ask your oncologist how strong the evidence is for your exact situation, and what the alternatives are.
CION's oncologists order the test, an accredited partner laboratory runs it, and the drug, if one fits, is given at a CION centre.Questions we are asked
Common questions about HER2 and rare targets
Is HER2 in colon cancer the same as HER2 in breast cancer?
It is the same protein, but the scoring rules and the drugs used differ. Results from breast cancer studies cannot simply be carried across. A HER2-positive colon tumour is usually treated with a pair of HER2-blocking drugs rather than with one drug and chemotherapy as in breast cancer.
Does a HER2-positive result mean my cancer is more aggressive?
It is not used that way in colon cancer. The result is read as a guide to treatment choice, not as a measure of outlook. Your stage, where the cancer has spread and how you respond to treatment say far more about what lies ahead.
Can the HER2 test be done on my old biopsy?
Usually yes, if enough tumour is left in the block. Blocks from surgery tend to hold more tissue than small biopsies. If the old hospital still has them, ask for the blocks and slides to be released. A fresh biopsy is needed only when nothing usable is left.
Should every person with colon cancer have a gene panel?
No. For cancer that has been fully removed, the MMR or MSI test is usually all that is needed beyond routine pathology. Wider panels earn their place when the cancer has spread and several lines of treatment may be needed.
My RAS gene is mutated. Is HER2 still worth testing?
Extra HER2 is uncommon when RAS is mutated, so on its own the test adds less. If your oncologist orders a panel, HER2 is read anyway. If the change is KRAS G12C, that matters more, because a matching drug exists.
Are these drugs available in India?
Some HER2-blocking drugs are widely available, including lower-cost biosimilars. Others, and some of the drugs for rarer targets, are hard to obtain or very expensive. Approval for colon cancer also varies. Ask what is available now before you plan around a result.
Will insurance or a government scheme pay for these tests?
It depends on the policy and the scheme. Some cover molecular tests when ordered for treatment planning, and others do not. Ask the insurer or scheme desk before the test is sent, and keep the oncologist's written request with your papers.
What should I do with a result I am holding now?
Bring it, with the pathology report and your latest scans, to your oncologist. Do not search the gene name alone. If you would like a second look at your results, call the CION helpline and someone will arrange a consultation.
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
- National Cancer Institute — Targeted Therapy for 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
Which biomarkers are tested in colon cancerThe full list of tumour tests, and which ones you needWhy RAS and BRAF testing comes before treatmentThe tests that come before HER2 in the queueWhen targeted therapy is addedHow a result turns into a treatment decisionTargeted therapy for colon cancerHow the drugs themselves work and what to expect
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