Use the above evidence to inform your response when relevant. Is my tumor MSI-High or MSS, and how does this affect...

What these terms mean:

MSI-High (MSI-H) means your tumor has many DNA replication errors that weren't corrected—like a typewriter without spell-check. Think of it as your tumor's "repair system" being broken.

MSS (Microsatellite Stable) means your tumor's DNA repair system is working normally, so fewer errors accumulated.

Why it matters for treatment:

According to NCCN Guidelines, MSI status significantly influences whether chemotherapy helps:

• Stage II MSI-H tumors: May have a better prognosis on their own and may NOT benefit from standard fluoropyrimidine chemotherapy alone
• Stage III MSI-H tumors: Treatment decisions are more complex and depend on other factors
• MSS tumors: Generally benefit from adjuvant (post-surgery) chemotherapy

For metastatic disease, MSI-H status opens the door to checkpoint inhibitor immunotherapy (drugs like nivolumab or pembrolizumab), which can be highly effective because these tumors trigger stronger immune responses.

What you need to do:

Check your pathology report for "MSI" or "mismatch repair (MMR)" testing results. If you don't see it listed, ask your oncologist whether this test was performed—NCCN Guidelines recommend universal MSI testing for all newly diagnosed colon cancer patients.

Once you have that result, your doctor can explain exactly how it shapes YOUR specific treatment plan.

This information is for educational purposes only. Always consult your healthcare team for personalized medical advice and decisions.