Colon Cancer Biomarkers
RAS mutation status (KRAS/NRAS) and mismatch repair testing (MSI-H/dMMR) must be completed before any treatment begins — they directly determine which drugs can and cannot help.
Reviewed by XpertPatient Medical Advisory · Updated June 2026 · Sources: NCI · ACS · ASCO · NIH/PMC
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What is a biomarker?
A biomarker is a measurable signal in your tumor. In colon cancer, biomarker tests tell your doctor which drugs will work for your specific cancer — and which ones won’t, no matter how promising they look.
In colon cancer, certain biomarker tests must be done before treatment begins. Using the wrong drug on the wrong tumor doesn’t just fail — it exposes you to side effects for no benefit. Your results protect you from that.
What this means for you: Two tests matter most before starting colon cancer treatment: RAS mutation status and mismatch repair (MSI) status. Make sure you have both results before treatment begins.
The Tests Your Doctor Orders
🔍 Do you have a mutation that blocks certain targeted drugs from working?
RAS mutations are found in about 50% of colon cancers. If your tumor has one, drugs like cetuximab and panitumumab will NOT work and should not be used. Knowing this before treatment protects you from ineffective therapy.
🔍 Does your cancer respond exceptionally well to immunotherapy?
About 15% of colon cancers are MSI-H. This is important — MSI-H colon cancer responds very well to immunotherapy with pembrolizumab, which is now approved as a first-line treatment for MSI-H metastatic colon cancer.
🔍 Is there a specific mutation linked to more aggressive disease?
BRAF V600E is found in about 10% of colon cancers. There’s now a targeted combination — encorafenib plus cetuximab — that works specifically for BRAF-mutated colon cancer.
Watch & Learn
Common Questions
Colon Cancer Biomarkers — Your Questions Answered
What does RAS wild-type mean?
It means your tumor does NOT have a RAS mutation. This is good news — it means you’re eligible for EGFR-targeting drugs like cetuximab, which can be added to chemotherapy for better results.
What is MSI-H colorectal cancer?
MSI-H means the cancer has a defect in its DNA repair system. These tumors respond very well to immunotherapy because the immune system can see and attack them more easily. Pembrolizumab is now a first-line option for MSI-H metastatic colorectal cancer.
Can I ask for biomarker testing if my doctor hasn’t ordered it?
Absolutely. Tell your doctor: ‘I’d like RAS, BRAF, and MSI/dMMR testing before we start treatment.’ These are guideline-recommended tests and most insurance plans cover them.
Should I get comprehensive genomic profiling?
Yes, especially for metastatic disease. Beyond RAS, BRAF, and MSI, there are rarer targetable mutations — like HER2 amplification and NTRK fusions — that comprehensive profiling can find.
Know Your Biomarkers. Own Your Journey.
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Visit the Colon Cancer Center → Full Biomarkers Guide →
