Blast cells are reduced through cancer treatments that target leukemia at its source, primarily chemotherapy, targeted drugs, and in some cases stem cell transplants. In healthy bone marrow, blasts make up about 5% of blood cells and shouldn’t appear in circulating blood at all. When blast counts reach 20% or higher in the bone marrow or blood, that signals acute leukemia, and the central goal of treatment is driving blasts back below 5%, which is the threshold for complete remission.
The specific approach depends on the type of leukemia, which genetic mutations are driving it, your age, and your overall health. Here’s what each major treatment does and how it works to bring blast counts down.
Intensive Chemotherapy
For most adults with acute myeloid leukemia (AML) who are healthy enough to tolerate it, treatment starts with intensive induction chemotherapy. The standard regimen combines two drugs: one that disrupts how leukemia cells copy their DNA, and an antibiotic-based drug that damages the DNA directly. This combination is given over a course of about ten days in the hospital, with seven days of one drug and three days of the other (often called the “7+3” regimen).
The goal of induction is to wipe out as many blast cells as possible in a single powerful course. After treatment, the bone marrow essentially empties out, and over the following weeks it begins to recover and produce normal blood cells again. Complete remission means the bone marrow biopsy shows fewer than 5% blasts, white blood cell and platelet counts return to functional levels, and the patient no longer needs blood transfusions. Not everyone achieves remission with the first round; some people need a second induction cycle. A bone marrow biopsy around day 14 helps doctors decide whether additional treatment is needed right away.
Lower-Intensity Options for Older Adults
Intensive chemotherapy isn’t safe for everyone. Older adults and people with significant health conditions often receive a gentler combination: a drug that interferes with how leukemia cells silence genes, paired with a newer oral medication that triggers cancer cell death by blocking a survival protein the cells depend on.
This combination has shown strong results. In a large clinical trial published in the New England Journal of Medicine, 66.4% of patients treated with this pairing achieved complete or near-complete remission, compared to just 28.3% for those receiving the gene-targeting drug alone. That’s a meaningful difference, and it has made this combination the standard of care for many patients who can’t tolerate intensive chemotherapy.
Targeted Therapies Based on Genetic Mutations
Not all leukemia is the same at the molecular level. Genetic testing of blast cells can reveal specific mutations that are fueling the cancer’s growth, and several FDA-approved drugs now target those mutations directly.
Two of the most important examples target mutations in genes called IDH1 and IDH2, which are found in a significant portion of AML cases. These mutations cause blast cells to produce an abnormal substance that blocks normal blood cell development. Drugs that inhibit IDH1 and IDH2 restore normal cell maturation, effectively forcing blasts to grow up into functioning blood cells instead of piling up in the marrow. The IDH1 inhibitor was approved in 2018 for patients whose leukemia returned after initial treatment, and in 2019 as a first-line option for newly diagnosed patients aged 75 and older or those unable to receive intensive chemotherapy.
Another common mutation affects a gene called FLT3, which acts like a stuck-on growth signal telling blast cells to multiply rapidly. Drugs that block this signal can be added to chemotherapy or used on their own. Because these targeted drugs work on specific molecular vulnerabilities, genetic testing at diagnosis is essential for matching you with the most effective treatment.
Emergency Measures for Very High Blast Counts
When white blood cell counts spike above 100,000 per microliter (normal is roughly 4,000 to 11,000), the sheer volume of blast cells can thicken the blood and block small blood vessels, particularly in the lungs and brain. This is called leukostasis, and it can cause serious breathing problems or neurological symptoms like confusion and vision changes.
In these situations, doctors may use a blood-filtering procedure called leukapheresis to physically remove blast cells from the bloodstream. The procedure works like dialysis: blood is drawn out, passed through a machine that separates and removes the excess white cells, then returned to the body. It can be repeated daily until the white cell count drops below the danger zone or symptoms resolve.
An oral medication called hydroxyurea is also commonly used as a bridge during this critical window. It works quickly to slow blast cell production and can be started immediately, even before the full treatment plan is in place. It’s typically given daily until blast counts fall to safer levels, buying time for definitive chemotherapy to begin.
Stem Cell Transplants
For patients at high risk of relapse, a stem cell transplant from a donor offers the best chance of long-term blast control. After chemotherapy reduces blasts to remission levels, the transplant replaces the patient’s bone marrow with a healthy donor’s immune system.
What makes transplants uniquely powerful is something called the graft-versus-leukemia effect. The donor’s immune cells recognize any remaining leukemia cells as foreign and attack them. Research has shown this immune effect can partly compensate even when the leukemia was initially slow to respond to chemotherapy. In patients whose blasts persisted early during induction but who eventually achieved remission, those who received a transplant had significantly better outcomes than those who did not. Without a transplant, the negative impact of that early blast persistence could not be overcome.
CAR-T Cell Therapy
For leukemia that returns after standard treatments, engineered immune cell therapy represents a newer option. In this approach, a patient’s own immune cells are collected, genetically modified in a lab to recognize specific proteins on the surface of blast cells, and then infused back into the body to hunt down and destroy the cancer.
In acute lymphoblastic leukemia (ALL), this technology targets a protein called CD19 found on the surface of leukemic blasts. For AML, researchers are developing versions that target other surface markers like CD123 and CLL-1. In an early clinical trial, five of eight pediatric AML patients treated with CLL-1 targeting therapy reached a leukemia-free state. Other targets under investigation include proteins that are overexpressed on leukemia stem cells but not on normal blood-forming cells, which could reduce side effects by sparing healthy bone marrow.
How Doctors Track Blast Reduction
Reducing blasts isn’t just about getting below 5% on a standard bone marrow biopsy. Doctors now use highly sensitive testing called measurable residual disease (MRD) analysis to detect tiny numbers of remaining leukemia cells that standard microscopy would miss. Using specialized flow cytometry, labs can identify abnormal cells at concentrations as low as 0.1%, and in some cases down to 0.02% to 0.05%.
The European LeukemiaNet currently defines MRD positivity at the 0.1% threshold, meaning even a tiny fraction of remaining blasts matters for predicting relapse risk. Some research suggests even lower thresholds, approaching 0.01%, may be the optimal cutoff for certain patient groups. MRD results after treatment help guide decisions about whether to proceed with a stem cell transplant, continue maintenance therapy, or adjust the treatment approach. Testing negative for MRD is one of the strongest predictors of long-term remission.