What is ctDNA testing and should Merkel Cell Carcinoma patients get it

Understanding ctDNA Testing for Merkel Cell Carcinoma

What is ctDNA Testing?

ctDNA stands for circulating tumor DNA — tiny fragments of cancer DNA that break away from tumors and circulate in your bloodstream. Think of it as a "liquid biopsy" — a blood test that detects cancer-related genetic material without needing a tissue sample.

When cancer cells die or break apart, they release DNA into the blood. By analyzing this DNA, doctors can:

• Detect cancer presence and disease burden (how much cancer is in your body)
• Monitor treatment response
• Identify recurrence (cancer coming back) before it shows up on imaging scans
• Guide surveillance and follow-up care

ctDNA Testing in Merkel Cell Carcinoma

According to the NCCN Guidelines for Merkel Cell Carcinoma (Version 2.2026), ctDNA testing has emerged as an important tool for MCC patients:

Key Clinical Uses:

1. Disease Assessment: ctDNA can assess disease burden in both virus-positive and virus-negative MCC patients (important because about 80% of MCC is associated with Merkel cell polyomavirus, but 20% is not)

2. Early Recurrence Detection: ctDNA typically becomes positive prior to or at the time of clinically evident recurrence — meaning it may detect cancer coming back before you or your doctor notice symptoms or see it on imaging

3. Surveillance Monitoring: For follow-up care, ctDNA testing is often obtained every 3 months to watch for signs of recurrence

4. Minimal Residual Disease (MRD): The test can detect minimal residual disease — very small amounts of cancer remaining after treatment

Should MCC Patients Get ctDNA Testing?

According to NCCN Guidelines, ctDNA testing should be considered as part of your initial workup and ongoing surveillance, particularly:

✅ Recommended for:

• Patients with stage III (nodal) or stage IV (metastatic) disease
• Post-treatment surveillance to monitor for recurrence
• Patients undergoing immunotherapy or radiation therapy (baseline testing helps track response)

Important Note: The NCCN Guidelines recommend that if your diagnosis was made only with a core biopsy, you should consider collecting additional tumor tissue (required for "tissue-informed" ctDNA testing) prior to immunotherapy or radiation therapy. This tissue-informed approach makes the blood test more accurate and personalized to your specific tumor.

Comparison with Other Biomarkers

MCC patients may also have access to MCPyV antibody testing (measuring antibodies to Merkel cell polyomavirus):

• Patients who test seronegative (no antibodies) have higher recurrence risk
• Rising antibody titers in seropositive patients may indicate early recurrence
• Baseline testing should be done within 3 months of treatment

ctDNA offers an advantage because it works for both virus-positive AND virus-negative MCC patients, making it more universally applicable.

Questions to Ask Your Oncology Team

1. Should I have ctDNA testing as part of my initial workup? (Especially important if you have stage III or IV disease)

2. Do you recommend tissue-informed ctDNA testing, and if so, when should we collect tumor tissue?

3. How often should I have ctDNA monitoring during surveillance? (The NCCN suggests every 3 months, but your specific schedule depends on your stage and treatment)

4. What will we do if my ctDNA becomes positive? (This helps you understand the clinical plan if early recurrence is detected)

5. Is ctDNA testing covered by my insurance, or are there costs I should know about?

6. How will you use ctDNA results to guide my treatment decisions?

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Key Takeaway

ctDNA testing represents an important advancement in MCC surveillance because it can detect recurrence earlier than traditional imaging, potentially allowing for earlier intervention. According to the NCCN Guidelines for Merkel Cell Carcinoma, this test should be part of the discussion with your care team, particularly for monitoring after treatment completion.

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

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Sources Cited:

• NCCN Guidelines for Merkel Cell Carcinoma (Version 2.2026) — specifically recommendations on ctDNA testing for disease assessment, recurrence detection, and surveillance
• Akaike T, et al. J Clin Oncol. 2024;42:3151–3161 — Clinical validation of ctDNA assay detecting MCC recurrence and minimal residual disease