If you live with polycythemia vera (PV), essential thrombocythemia (ET), or myelofibrosis (MF), you may have heard your doctor mention your “mutation” or “allele burden.” A new review takes a close look at MRD monitoring in MPN, and I want to walk you through it in plain language.
The review, by Gary Markey and Stephen Langabeer of the Cancer Molecular Diagnostics lab at St. James’s Hospital in Dublin, was published October 20, 2026, in the journal Cancers. It compares lab tests that find tiny amounts of disease that standard tests miss.
Key Points
- MRD testing looks for very small amounts of the mutations that drive your disease.
- It is not routine for every MPN patient. It is most actionable after a stem cell transplant and is also relevant after therapies such as interferon.
- A test called droplet digital PCR (ddPCR) currently appears to be the most practical tool for clinical decisions.
- Next-generation sequencing (NGS) gives a broader picture, but cost, slower turnaround, and lack of standardization limit its routine use for MRD.
- An “undetectable” result depends on which test was used.
- The authors call for standardized reporting and lab proficiency testing.
What Is MRD Monitoring in MPN?
MRD stands for measurable residual disease. The review defines it as disease-driving mutations that persist below the level standard clinical tests can pick up.
Think of it as a smoke detector far more sensitive than your nose. Your blood counts may look fine, yet a sensitive test can still find cells carrying your mutation. Tracking that over time may show how well treatment is working and help spot a relapse.
Most MPNs are driven by mutations in one of three genes: JAK2, CALR, or MPL. Together these are found in about 90% of MPN patients. JAK2 V617F alone shows up in more than 95% of people with PV. These mutations act as markers that can be measured again and again.
What Is Allele Burden?
Allele burden, also called variant allele frequency (VAF), is the percentage of your gene copies that carry the mutation. If 40 of every 100 copies of JAK2 carry V617F, your allele burden is 40%. MRD testing tracks this number at very low levels over time.
Why MRD Testing Isn’t Routine for Every MPN Patient
Unlike in acute leukemias, MRD testing is not routinely indicated for every MPN patient.
The reason: in many of us, the driver mutation stays detectable even when blood counts and symptoms are well controlled. A detectable mutation alongside good counts is common. That is why this type of monitoring is used selectively.
When MRD Monitoring in MPN Matters Most
According to the review, MRD testing is most relevant after certain therapies, such as allogeneic stem cell transplant and interferon. Transplant is where it is most actionable. The authors also note that MRD assessment can help gauge how deep a treatment response goes.
After a Stem Cell Transplant
Allogeneic stem cell transplant (ASCT), where you receive donor stem cells, is used most often in myelofibrosis. A rise in mutation levels on a lab test (molecular relapse) often comes before a clinical relapse.
European transplant recommendations for myelofibrosis (EBMT/ELN), cited in the review, support checking driver mutations at about 30, 100, 180, 270, and 360 days after transplant. Catching a problem early can allow an intervention such as donor lymphocyte infusion. Combining MRD results with chimerism testing, which measures how much of your blood comes from the donor, improves relapse detection.
After Interferon Treatment
The review also lists interferon therapy as a setting where MRD monitoring is relevant. For a full rundown, see Interferon Treatment for MPNs: What You Need to Know. The authors note that some additional mutations, such as DNMT3A, have been linked to interferon resistance and to not reaching a complete molecular response.
What About Ruxolitinib?
In a long-term follow-up of myelofibrosis patients on ruxolitinib, JAK2 V617F allele burden dropped over time, and some patients reached a partial or complete molecular response. Those drops tracked with a smaller spleen size. The authors say this supports using molecular monitoring as an added measure of treatment response.
What “Undetectable” Really Means
This is the part I wish every patient understood. An “undetectable” result does not always mean the mutation is gone. It means the mutation is below what that specific test can see.
- NGS can see down to about 1 to 2%.
- qPCR varies by lab, from about 1% down to 0.01%.
- ddPCR can see as low as about 0.01%.
So a result that is undetectable by NGS could still be measurable by ddPCR. Ask which test was used and what its limit of detection is. That number is often printed on your lab report.
When I reached complete molecular remission, one of the first questions I asked was, “By which test?” I share more about that in How I Achieved Complete Molecular Remission from PV.
What to Ask Your Care Team
Bring these to your next appointment. They come straight from the review’s findings.
- Does MRD testing apply to me? Ask whether your situation, such as transplant or interferon treatment, is one where monitoring is useful.
- Which mutations am I being tracked for? JAK2 V617F, JAK2 exon 12, CALR, MPL, or none of these?
- Which test does my lab use, and what is its limit of detection? qPCR, ddPCR, or NGS? Each has different sensitivity.
- What is my current allele burden, and how has it changed? The trend often tells you more than a single number.
- If I’ve had a transplant, how often will you check? Ask whether your center follows a schedule like days 30, 100, 180, 270, and 360, and whether chimerism is checked too.
- Do I have other mutations? Ask whether an NGS panel has looked for mutations that might affect how you respond to treatment. The review notes that in PV, resistance to hydroxyurea was estimated in 64% of patients with TP53 mutations and 49% of those with spliceosome or chromatin gene mutations.
- What would a rising result mean for me? Know the plan before you see the number.
If you don’t have an MPN specialist yet, our MPN specialists and treatment centers page can help.
The Tests, Explained in Plain Language
The review compares three main tools. For unfamiliar terms, see the PV Reporter MPN Cancer Dictionary.
qPCR: The Established Workhorse
Quantitative PCR (qPCR) copies a small piece of DNA many times so the lab can measure how much mutation is present. It has been widely used for years.
ddPCR: The Sharpest Tool for Now
Droplet digital PCR splits your sample into many tiny droplets and tests each one, so it can count very low mutation levels accurately. In one study cited, ddPCR detected JAK2 V617F down to 0.01%, compared with 0.12% for qPCR. Another study found both could reach 0.01%, but larger comparisons showed ddPCR gave more precise and reproducible results.
The authors concluded that ddPCR currently appears the most practical tool for clinical decisions because of its high sensitivity, relatively low cost, and ability to measure driver mutations.
NGS: The Wide-Angle Lens
Next-generation sequencing reads many genes at once. Its sensitivity for driver mutations is about 1 to 2%, lower than ddPCR. But it can find “extra” mutations that help predict risk and treatment resistance.
That matters because if an MPN turns into acute leukemia, the new disease can come from a different clone. Tracking one driver mutation could underestimate what is going on. NGS can track driver and non-driver mutations together.
Does Your Mutation Type Matter?
Yes. Your mutation shapes how monitoring can be done.
- JAK2 V617F: ddPCR works well and is the best-studied option.
- JAK2 exon 12: A small share of PV patients carry exon 12 mutations instead of V617F. More than 60 different exon 12 mutations have been identified, so sequencing is the gold standard. The review lists no standard ddPCR test for them.
- CALR: ddPCR works well for the common type 1 and type 2 mutations. A CALR ddPCR test predicted relapse after transplant in primary myelofibrosis.
- MPL: These mutations are less common and more varied, which has limited their use as an MRD marker.
- Triple-negative: About 15% of ET and 10% of PMF patients have no JAK2, CALR, or MPL mutation. For them, other mutations can serve as markers. In one transplant study cited in the review, ddPCR tracked IDH1, IDH2, and DNMT3A mutations to help identify relapse.
Why It Matters
Treatments like ruxolitinib and interferon have improved symptoms and spleen size for many of us, but deep molecular responses remain limited. Researchers are now testing combination therapies, and the authors say MRD monitoring would help measure how well they work.
To me, that is the big picture. MRD monitoring in MPN could help shift care from controlling symptoms toward precision-guided management. We are not there yet, and standardized testing is still needed, but it is a hopeful direction.
Talk with your hematologist about whether MRD testing is right for you. For more, visit PV Reporter or read the National Cancer Institute’s MPN treatment overview.
About the Author
David Wallace is a nationally recognized myeloproliferative neoplasm (MPN) patient advocate, writer, and the founder and publisher of PV Reporter. He also founded MPN Cancer Connection, a 501(c)(3) nonprofit organization, and serves as its executive director. Diagnosed with polycythemia vera in 2009 and now in complete molecular remission, David has spent more than a decade helping patients understand MPN research, treatment options, and the questions to ask their healthcare teams. His work brings the patient voice into discussions with clinicians, researchers, and industry leaders.
Medical Disclaimer
This article is for educational purposes only and is not medical advice. It does not replace consultation with a qualified hematologist or MPN specialist. Discuss all diagnosis and treatment decisions with your healthcare team.
References
Markey GE, Langabeer SE. Measurable Residual Disease (MRD) Monitoring in Myeloproliferative Neoplasms. Cancers. 2026;18(20):3397. Published October 20, 2026. https://doi.org/10.3390/cancers18203397
