Chronic myeloid leukemia is a slow-growing type of leukemia. It rarely transforms into more aggressive forms such as acute myeloid or acute lymphoid leukemia.

Chronic myeloid leukemia (CML) is a slow-growing type of leukemia that makes up about 30% of adult leukemias. The 10-year survival rate has improved from about 20% in the 1970s to about 85% today.

Acute myeloid leukemia (AML) is the most common form of leukemia. It tends to be more aggressive, and only about 30% of people with AML are alive 5 years after their diagnosis.

CML can transform into a CML blast crisis before progressing to AML or other forms of aggressive leukemia. The chances of CML transforming are low if you receive proper treatment.

Read on to learn more about the progression of CML to AML and other forms of leukemia.

Unlike many other types of cancer, CML isn’t divided into stages. Instead, medical professionals divide leukemia into three phases based on how many blasts are in your bloodstream. Blasts are immature and abnormal blood cells that can crowd out healthy cells.

The three phases of CML are:

  1. Chronic phase: Less than 10% of the cells in the blood and bone marrow of people in the chronic phase are blast cells. Symptoms are generally mild or not apparent. About 95% of people receive a diagnosis in the chronic phase.
  2. Accelerated phase: Blasts make up 10–19% of cells in the bloodstream and bone marrow of people in the accelerated phase. Symptoms in this phase tend to be more severe and may include:
  3. Blast phase: More than 20% of cells in the blood and bone marrow of people in the blast phase are blast cells. Symptoms in this phase tend to be more severe.

The blast phase goes by several other names such as:

  • blast crisis
  • blastic phase
  • blast transformation
  • acute phase

CML progression

Without treatment, chronic phase CML progresses to the blast phase in 3–5 years. Many people who receive treatment never progress to the blast phase.

Researchers in a 2017 study found that less than 5.8% of people receiving imatinib (a type of cancer growth blocker called a tyrosine kinase inhibitor) progressed to the blast phase at a 10-year follow-up.

CML in the blast phase can transform into acute leukemia. Acute leukemias tend to be more aggressive than chronic leukemias and can result in a poorer outlook.

Types of acute leukemia CML can transform into

Blood cells are created by stem cells in your bone marrow. These cells create two types of cells:

  1. myeloid progenitor cells that become platelets, red blood cells, and some white blood cells
  2. lymphoid progenitor cells that become other types of white blood cells

CML can transform into several types of acute leukemia depending on which type of abnormal cell builds up in your blood.

  • Acute myeloid leukemia: In about 60–80% of cases, the CML blast phase is characterized by the buildup of abnormal myeloid cells, and AML develops.
  • Acute lymphoblastic leukemia: In about 20–30% of cases, the blast phase is characterized by the buildup of lymphoid cells, and acute lymphoblastic leukemia (ALL) develops. It’s thought that a buildup of a molecule called interleukin 6 may be associated with the transformation of CML to ALL.
  • Acute biphenotypic leukemia: In about 6–10% of cases, the CML blast phase is characterized by a buildup of both types of cells. When this happens, the resulting leukemia is called acute biphenotypic leukemia.

Myeloid sarcoma is a rare cancer that develops in immature myeloid cells. It causes a tumor to form anywhere in your body outside of the bone marrow. CML can potentially develop into myeloid sarcoma, although it’s been uncommon since the development of tyrosine kinase inhibitors in the early 2000s.

Common locations where myeloid sarcoma develops include:

  • bone
  • skin
  • lymph nodes

Myeloid sarcoma can develop spontaneously or develop from CML or AML.

People with CML seem to be at an elevated risk of developing some types of cancer compared with the general population. According to the American Cancer Society, the risk seems to be highest in the 5 years after CML diagnosis.

Cancers that people with CML are at an elevated risk of developing include:

Researchers still aren’t sure exactly why people with CML may be at an increased risk of developing some cancers. In a 2018 study, researchers found evidence that the increased risk is linked to the cancer itself and not the tyrosine kinase inhibitors used to treat it.

It’s essential to see a doctor as soon as possible if you have potential symptoms of leukemia such as unexplained fatigue or weight loss. Receiving prompt treatment, attending all your scheduled follow-ups, and following your treatment schedule gives you the best chance of avoiding progressing to the blast phase.

You can reduce your risk of developing a second cancer by:

  • avoiding tobacco and tobacco smoke
  • getting to and maintaining a moderate weight
  • staying physically active
  • eating a balanced overall diet
  • avoiding alcohol or limiting alcohol to one drink a day for women or two drinks per day for men

It’s especially important for people with CML to undergo regular cancer screenings.

Language matters

You’ll notice that the language used to share stats and other data points is pretty binary, fluctuating between the use of “men” and “women.”

Although we typically avoid language like this, specificity is key when reporting on research participants and clinical findings.

Unfortunately, the studies and surveys referenced in this article didn’t report data on, or include, participants who were transgender, nonbinary, gender nonconforming, genderqueer, agender, or genderless.

CML is a slow-growing type of leukemia that develops in cells that produce red blood cells, platelets, and some white blood cells. People with CML usually have a good outlook, but a small number of people progress to the blast phase.

The blast phase is the most aggressive phase of CML. Blast phase CML can progress to AML or other aggressive leukemias. Most people who receive proper treatment never progress to the blast phase.