What is Chronic Myeloid Leukemia?

Chronic myeloid leukemia (CML) is a type of cancer that starts in certain blood-forming cells of the bone marrow. In CML, a genetic change takes place in an early (immature) version of myeloid cells - the cells that make red blood cells, platelets, and most types of white blood cells (except lymphocytes). This change forms an abnormal gene called BCR-ABL1, which turns the cell into a CML cell. The BCR-ABL1 gene is formed by a translocation between parts of chromosomes 9 and 22 in a single bone marrow cell during cell division. The abnormal chromosome 22 is called the "Philadelphia chromosome" (Ph chromosome). The CML cells grow and divide, building up in the bone marrow and spilling over into the blood. In time, the cells can also invade other parts of the body, including the spleen. CML is a fairly slow-growing leukemia, but it can also change into a fast-growing acute leukemia that is hard to treat.

Types of Chronic Myeloid Leukemia

Chronic myeloid leukemia is typically classified into three phases based on the severity and progression of the disease. These phases are:

Chronic phase: This is the earliest phase where the number of immature white blood cells (blasts) in the blood and bone marrow is fairly low. Patients in this phase usually have fewer symptoms and respond better to treatments.
Accelerated phase: In this phase, the number of blasts in the blood and bone marrow increases. Symptoms may be more severe and the disease becomes harder to control.
Blast phase (or crisis phase): This is the most severe phase of CML, where the number of blasts continues to increase. It behaves like acute leukemia with symptoms worsening rapidly. This phase is difficult to treat and is often fatal.

Why Do People Get Chronic Myeloid Leukemia?

The exact cause of CML is unknown. However, it's clear that something happens to cause a genetic mutation in the DNA of cells that produce blood. The mutation causes the cells to produce an enzyme called tyrosine kinase that promotes excessive growth of white blood cells. It's not clear what causes this mutation. CML is not inherited, but appears to develop randomly in people. Certain factors may increase the risk of developing CML, such as exposure to high levels of radiation and being older, particularly being over the age of 60.

Who Gets Chronic Myeloid Leukemia?

According to the National Cancer Institute, there will be an estimated 8,930 new cases of CML in 2023, making up 0.5% of all new cancer diagnoses. In 2020, there were an estimated 66,366 people living with CML in the United States. Approximately 0.2% of men and women will be diagnosed with CML at some point during their lifetime, based on 2017-2019 data. The average age at diagnosis of CML is around 64 years. This type of leukemia is rarely seen in children. CML is slightly more common in males than females.

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Types of Chronic Myeloid Leukemia

Chronic myeloid leukemia is typically classified into three phases based on the severity and progression of the disease. These phases are:

Chronic phase: This is the earliest phase where the number of immature white blood cells (blasts) in the blood and bone marrow is fairly low. Patients in this phase usually have fewer symptoms and respond better to treatments.
Accelerated phase: In this phase, the number of blasts in the blood and bone marrow increases. Symptoms may be more severe and the disease becomes harder to control.
Blast phase (or crisis phase): This is the most severe phase of CML, where the number of blasts continues to increase. It behaves like acute leukemia with symptoms worsening rapidly. This phase is difficult to treat and is often fatal.