Blast crisis is the third phase of chronic myeloid leukemia (CML) and the most difficult to treat. New types of targeted therapy have improved the treatment and outlook for people in all phases of CML.

Chronic myeloid leukemia (CML) is a type of blood cancer that makes up about 15% of leukemias. It’s a slow growing cancer that starts in the cells in your bone marrow that become:

  • certain types of white blood cells
  • red blood cells
  • platelets

CML causes your body to produce too many abnormal and immature blood cells called blasts. These abnormal cells can crowd out the production of healthy blood cells.

Doctors don’t stage CML like most types of cancer but instead divide it into three phases depending on how many abnormal cells your body produces:

  • the chronic phase
  • the accelerated phase
  • blast crisis

Blast crisis is the third phase of CML and the most difficult to treat. Recent advances in a type of targeted therapy called tyrosine inhibitors have greatly improved the outlook for people with CML in general and moderately improved the outlook for people in blast crisis.

Read on to learn more about blast crisis in CML, including how it’s defined, its symptoms, and how it’s treated.

Disease progression in chronic myeloid leukemia (CML)Share on Pinterest
Disease progression in chronic myeloid leukemia (CML). Medical Illustration by Brittany England

Blast crisis is the third phase of CML. All untreated people will eventually progress to the blast phase, although not necessarily in a uniform order. Doctors primarily determine what phase your CML is in based on the number of blasts in your bone marrow and blood.

CML tends to develop slowly. It isn’t staged like most types of cancer. Doctors divide it into three phases instead.

Chronic phase

Most people with CML receive a diagnosis in the chronic phase. People in this stage usually don’t experience symptoms or experience very mild symptoms. Without treatment, the chronic phase of CML progresses to the accelerated phase within roughly 3 to 5 years. Some people progress directly to blast crisis.

People in the chronic phase have less than 10% blasts in their blood and bone marrow samples.

Accelerated phase

The accelerated phase usually lasts about 3 to 9 months.

People are in the accelerated phase if they have more than 15% blasts in their blood and bone marrow samples. People in this phase may start to develop general symptoms such as:

  • fever
  • poor appetite
  • weight loss

About 4 to 5% of people with CML receive a diagnosis when they’re in the accelerated phase.

Blast crisis

Blast crisis is the third phase and the hardest to treat. In this phase, the cancer starts to act like a more aggressive type of leukemia called acute myeloid leukemia (AML). About 1 to 2% of people receive a diagnosis of CML in blast crisis.

You’re considered to be in the blast crisis if your blood and bone marrow samples contain more than 20% or 30% blasts, depending on which classification system is used. The World Health Organization uses 20% as a cutoff.

Symptoms are generally more severe than in previous phases, and leukemia may spread to other organs such as:

  • lymph nodes
  • bones
  • skin
  • testis
  • nervous system

AML and CML in blast crisis

AML is a more aggressive type of leukemia. CML in blast crisis can act like AML, but identifying which leukemia you have is important for deciding on the best treatment options.

Doctors can differentiate them by identifying a certain genetic mutation called the Philadelphia chromosome that’s present in almost all people with CML but is rare among people with AML.

Learn more about AML.

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Blast crisis can cause symptoms such as:

Blood and other tests may reveal signs such as:

  • high white blood cell count
  • very high or low platelet count
  • blast cells that have spread to other organs
  • new chromosome abnormalities in cancerous cells

When deciding how to treat CML in a blast crisis, doctors consider factors such as:

  • whether your cancer has returned after treatment
  • whether you have elevated levels of abnormal myeloid cells or abnormal myeloid and lymphoid cells
  • which tyrosine kinase inhibitors you’ve been exposed to
  • whether you have a BCR-ABL1 gene mutation
  • whether you’re a candidate for intensive chemotherapy and a stem cell transplant

According to the National Cancer Institute, treatment for blast crisis in CML may include:

Tyrosine kinase inhibitors improving treatment and outlook

The development of tyrosine kinase inhibitors has revolutionized treatment over the last 20 years. These medications are taken as pills. Chemicals in these drugs specifically target cancer cells while minimizing damage to healthy cells. They may be administered alone or along with traditional chemotherapy.

Tyrosine kinase inhibitors you may receive include:

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Learn more about treatment options for CML by phase.

The overall 5-year survival rate for CML has risen from 33% to more than 90% since the development of tyrosine kinase inhibitors, and the 10-year survival rate has risen from 11% to 84%.

People in the blast crisis phase of CML have a poorer outlook than people in earlier phases. In a 2019 study, researchers found that the median survival time for people in blast crisis was 1.8 years, compared to 6 years for people in the accelerated phase of CML.

Researchers are continuing to investigate how to best treat advanced CML, and it’s likely that the survival rate will continue to increase in the future.

Blast crisis is the final phase of CML. A doctor may diagnose blast crisis if you have more than 20% or 30% abnormal cells in your bone marrow and blood samples.

A type of targeted therapy called has drastically improved the outlook for people with CML. Tyrosine kinase inhibitors are often administered alone or combined with other treatments such as chemotherapy.