Chronic myeloid leukemia (CML) is a blood and bone marrow cancer. It results in the production of too many immature blood cells, called myeloblasts. Doctors can classify CML into 3 phases using lab tests to determine the amount of immature white blood cells present in the blood or bone marrow.

In CML, there is an abnormal overproduction of myeloblasts, which are a type of immature blood cell that makes white blood cells (WBC) called myeloid cells. As the amount of these immature blood cells increases, it leaves less room for healthy blood cells. This results in the symptoms of CML.

Unlike other types of cancer, doctors can describe the progression of CML using 3 phases — chronic, accelerated, and blast. Each phase differs in the number of blast cells in their blood or bone marrow, has a different outlook, and entails a different treatment approach.

In this article, we will discuss how different phases of CML may appear in lab tests, as well as treatment options for CML.

A person performing laboratory tests to check for CML.Share on Pinterest
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Many people with CML may be asymptomatic and receive a diagnosis of CML following blood tests for an unrelated health problem or during a routine lab examination.

If a doctor suspects CML, they may initially perform a physical exam and ask questions about health, before requesting a number of lab tests, which can include:

  • complete blood count with differential
  • peripheral blood smear
  • bone marrow aspiration and biopsy
  • cytogenetic analysis
  • fluorescence in situ hybridization (FISH)
  • polymerase chain reaction (PCR) test

These tests can help identify abnormal shape, size, or amount of blood cells, and check for CML markers, such as the Philadelphia chromosome (also known as BCR-ABL1). For people in the chronic phase, blood tests would reveal fewer than 10% of cells in the blood and bone marrow are blast cells. They may also have anemia.

A person may meet the criteria for the accelerated phase if they present with any of the following:

  • 15-30% of blasts in blood or bone marrow
  • low platelet count
  • 20% or more basophils
  • additional abnormalities in the Philadelphia positive (Ph+) cells

Additional findings may include persistent spleen enlargement that does not respond to treatment and cytogenetic evolution, showing other chromosomal abnormalities in the Philadelphia (Ph+) cells.

In the blast phase, there are 30% or more blasts in both blood or bone marrow. There may also be an extramedullary proliferation of blasts, spreading in the bone, lymph nodes, skin, and central nervous system. Bone marrow biopsy also shows large clusters of blasts.

A person’s treatment is highly individualized and may vary depending on their CML phase and other health issues. Treatment options may include:

Targeted therapy

This type of treatment uses drugs or other substances to identify and target specific cancer cells. It is typically the first line of treatment for CML.

Tyrosine kinase inhibitors (TKIs) are an effective targeted therapy for treating CML. TKIs block the action of tyrosine kinase enzymes, which are responsible for causing stem cells to develop into more WBCs that the body requires. Blocking these enzymes can prevent cancer cells from growing.


Chemotherapy is a type of cancer treatment that uses drugs to slow or stop the growth of cancer cells. People typically receive chemotherapy by mouth or injected into a vein or muscle. Chemotherapy was the primary treatment for CML. However, doctors will now typically only recommend chemotherapy if a person is undergoing a stem cell transplant or does not respond well to TKIs.


Immunotherapy is a type of treatment that trains a person’s immune system to fight cancer. It uses substances to either stimulate or suppress the immune system to aid against cancer.

High-dose chemotherapy with stem cell transplant

While high doses of chemotherapy can help kill cancer cells, they may also destroy healthy blood cells. In these cases, people may receive a stem cell transplant to help enable the body to replace damaged blood cells with healthy ones. This is because stem cells have the potential to turn into many other types of cell and can grow and restore the body’s blood cells.

Donor lymphocyte infusion (DLI)

DLI is a type of treatment that a person may receive after a stem cell transplant. It uses lymphocytes, a type of WBC, from a donor and infuses them into the person with CML. The lymphocytes recognize the cancer cells as foreign and attack them.


In cases where people experience spleen enlargement, they may require surgery to remove the spleen.

Click here to learn more about treatment options for CML.

People in the chronic phase may or may not have symptoms. When present, symptoms are usually relatively mild and may result from underlying anemia and spleen enlargement. They can include:

  • fatigue
  • anemia
  • unexplained weight loss
  • night sweats
  • loss of appetite feeling full easily
  • pain in the upper left abdomen, below the ribs, due to an enlarged spleen
  • blurred vision
  • unusual or excessive bleeding
  • priapism

People may stay in the chronic CML phase for years or longer or undergo remission when managed with treatment. However, lack of treatment may cause it to progress. A 2018 review states that most chronic CML evolves into the accelerated phase before the blast phase. However, 20% of people may transition directly into the blast phase.

Symptoms for the accelerated phase are typically similar to chronic. However, they may include bone pain.

In addition to the above symptoms, a person in the blast phase of CML may also notice additional symptoms, such as:

  • fever
  • bone pain
  • bruising more easily than normal
  • repeated infections
  • swollen lymph nodes

Since the introduction of TKIs in the treatment of CML, treatment outcomes have significantly improved, with some evidence suggesting a 5-year survival of roughly 90%. This is consistent with other research, which indicates a 10-year survival increase from 11 % to roughly 84%.

A 2020 article notes that the 7-year survival for people living with CML and taking Imatinib, a TKI, is roughly 87.7%. However, it adds that the rate decreases for people in accelerated and blast phases with a 7-year survival of 77.5% and 53%, respectively.

Several other factors may also affect the outlook of a person with CML. A 2016 study found that multiple chromosomal changes in CML cells are associated with poor outcomes. Other factors linked to poor outcomes can include:

  • older age (>60)
  • spleen enlargement
  • high number of blast cells
  • very high or low platelet counts
  • bone damage from CML
  • increased eosinophils and basophils in the blood

CML is a bone and blood marrow cancer that results from an overproduction of WBCs.

Unlike other types of cancer, doctors use phases rather than stages to describe the progression of CML. Each phase differs with increasing numbers of blast cells as the condition progresses. A person’s CML phase plays a huge part in their treatment and outlook.