Biomarker Resource Center
Rectal Cancer Biomarkers
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 signal your cancer leaves behind. Doctors find these signals in your blood or tumor tissue. The signals tell your doctor important things — like what type of cancer you have and how it is behaving.
Think of it like a clue. Your doctor collects clues from your biomarker test results. Those clues help build a picture of your cancer. That picture helps your doctor and you have a more informed conversation about next steps.
Everyone’s cancer is different — even people with the same type of cancer can have very different results. That is why biomarker testing matters. It helps your care team understand your cancer specifically.
For Rectal Cancer
Why do biomarkers matter in rectal cancer?
Biomarker testing in rectal cancer gives your doctor important information before care decisions are made. Two markers matter most: MSI status and RAS mutation status. Together they help your doctor have a more informed conversation with you about your care. Ask your doctor whether both have been tested.
💬 A good question to ask your doctor: Ask your doctor for your MSI result and your RAS result. These two pieces of information are important starting points for conversations about rectal cancer care.
The most important rectal cancer biomarkers are MSI status and RAS mutation status. Together they tell your doctor which treatment approaches are likely to help and which are not, before care decisions are made.
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Have you had biomarker testing for your rectal cancer?
The Tests Your Doctor May Order
🔍 How does your tumor’s DNA repair system work?
MSI-H means your tumor has a change in how it repairs DNA. This is found in a small percentage of rectal cancers. It is an important finding that your doctor will use as part of the conversation about your care. Ask your doctor whether MSI testing has been done and what your result means.
🔍 Does your tumor have a mutation that affects which approaches may help?
RAS mutations are found in about half of rectal cancers. This result gives your doctor important information about which approaches are likely to be useful. Ask your doctor what your RAS result means for your care.
🔍 Is a protective gene changed in your tumor?
TP53 changes give your doctor information about how your cancer may be behaving. Ask your doctor whether TP53 was tested and what the result means for your care conversation.
Watch & Learn
Important: This page is for education only. It is not medical advice. Every patient’s situation is different. Please talk to your doctor or care team about what your biomarker results mean for you specifically.
Common Questions
Rectal Cancer Biomarkers — Your Questions Answered
What does MSI-H mean for rectal cancer?
MSI-H is a finding that your doctor will use as part of the conversation about your rectal cancer care. If your tumor is MSI-H, ask your doctor what approaches are commonly discussed for this finding and whether a specialist referral makes sense.
What is the watch-and-wait approach?
Watch-and-wait is an approach that some rectal cancer patients may discuss with their care team depending on their situation and response. Ask your doctor whether this is something worth discussing for your specific case.
Should I seek care at a specialist center?
Many patients with rectal cancer benefit from being seen by a team that includes a colorectal surgeon, radiation oncologist, and medical oncologist. Ask your doctor or the Fight Colorectal Cancer organization at fightcolorectalcancer.org for help.
Is there a patient support community for rectal cancer?
Yes. Fight Colorectal Cancer at fightcolorectalcancer.org is a trusted resource for patients and families. The Colorectal Cancer Alliance at ccalliance.org is another helpful resource.
Quick Links
From the Rectal Cancer Center on XpertPatient
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Visit the Rectal Cancer Center → Full Biomarkers Guide →
