The Bone Marrow Response Gap
Historically, doctors have looked to the bone marrow to answer that question. If a bone marrow biopsy shows fewer abnormal blast cells (immature, cancerous cells) after treatment, that is generally considered a positive sign. But bone marrow biopsies are invasive, and they tell only part of the story.
What happens in the blood circulating through your veins may be just as telling — possibly more so.
This study analyzed data from 120 patients in the DACOTA trial, a clinical trial that randomized CMML patients to receive one of two treatments: decitabine (a chemotherapy drug that works partly by reprogramming cancer cells) or hydroxyurea (a drug that slows rapidly dividing cells). Patients were evaluated after three and six cycles of treatment with blood counts and bone marrow assessments.
The Numbers That Changed the Calculus
The researchers tracked two key measurements in the blood: total white blood cell (WBC) count and circulating monocytes (a type of white blood cell that is abnormally elevated in CMML). They also used flow cytometry — a lab technique that sorts and counts specific cell types in a blood sample — to track two more precise markers: classical monocytes and immature granulocytes (young, abnormal white blood cells that spill out of the bone marrow before they are mature).
What they found was striking. Patients who still had elevated white blood cell counts or high monocyte levels after six treatment cycles faced more than five times the risk of dying compared to patients whose counts had come down — regardless of what the bone marrow biopsy showed, and regardless of which treatment they received.
This does not mean that bone marrow testing is no longer useful — it means blood counts may add important information on top of it.
The two flow cytometry markers — classical monocytes and immature granulocytes — were also independently predictive of survival even earlier, after just three cycles of treatment. Patients with both markers below specific thresholds had a median survival of about 35 months, compared to roughly 15 months for everyone else. That is a meaningful difference.
Why This Finding Matters for Patients and Doctors
Right now, there is no consensus on what "good response" looks like in CMML treatment beyond bone marrow findings. If circulating blood counts turn out to be reliable, easy-to-track indicators of prognosis, they could guide treatment decisions more quickly and less invasively. Instead of waiting for a bone marrow biopsy, a regular blood draw might tell doctors — and patients — whether the current treatment approach is working.
If you or a loved one has been diagnosed with CMML, it is worth asking your hematologist (blood cancer specialist) about what markers they are tracking and what the counts mean at each evaluation point.
The study has real limitations to keep in mind. It analyzed data from a single clinical trial with 120 patients — a relatively small number for a cancer study. CMML is rare enough that large trials are hard to run. The study also cannot yet say whether actively working to push blood counts below those thresholds — by adjusting treatment — would improve survival, or whether the low counts are simply a sign that treatment is already working well in patients who were going to do better anyway.
That distinction matters enormously. Future research needs to test whether treatment strategies specifically targeting these blood count thresholds — cytoreduction goals built around circulating monocytes and granulocytes — translate into longer lives for CMML patients. If they do, it would represent a meaningful shift in how this difficult disease is monitored and managed.