Chronic myeloid leukemia (CML) is one type of cancer of the bone marrow and blood. It is also called chronic myelogenous leukemia or chronic myelocytic leukemia.
What is chronic myeloid leukemia?
Leukemia begins in the bone marrow.
- In CML, too many blood stem cells become granulocytes — a type of white blood cell.
- The abnormal granulocytes, also called CML or leukemia cells, grow and survive better than normal cells.
- Over time, they crowd out healthy cells your body needs.
Acute leukemia quickly prevents a large proportion of early blood cells from maturing. In chronic leukemia, like CML, more healthy blood cells get a chance to mature, so symptoms usually come on more gradually, and they are less severe at first.
Understanding your bone marrow and blood
To understand leukemia, it helps to know the basics about your bone marrow and blood cells.
What are stem cells?
Stem cells are cells in your body that have the potential to turn into any kind of cell, such as a skin cell, liver cell, brain cell or blood cell. Stem cells that turn into blood cells are called hematopoietic stem cells, or blood stem cells.
Why are blood stem cells important?
When blood cells become old or damaged, they die, and blood stem cells produce new blood cells to replace them. Blood stem cells are mainly found in bone marrow (the soft, spongy tissue inside your bones), but some are also found in circulating blood.
Blood stem cells produce myeloid stem cells and lymphoid stem cells.
- Myeloid stem cells produce myeloblasts, which in turn produce white blood cells known as granulocytes, as well as red blood cells and platelets.
- Lymphoid stem cells produce lymphoblasts, which in turn produce several types of white blood cells.
What do healthy blood cells do?
Healthy white blood cells, red blood cells and platelets are essential.
- White blood cells fight infection.
- Red blood cells carry oxygen from your lungs to other parts of your body and take carbon dioxide back to your lungs to be removed.
- Platelets make your blood clot and slow or stop bleeding.
Symptoms of CML
In the early stages, CML usually doesn’t cause symptoms, and it may take years before symptoms develop.
Symptoms of CML are often similar to the flu or other common, less serious diseases. Check with your doctor if you have any of these.
Symptoms from changes in white blood cell counts:
- Flu-like symptoms, such as fever, sweats and body aches
- Blurry vision or other vision changes
- Bone pain
Symptoms from low red blood cells:
- Shortness of breath
- Pale skin
- Fatigue, weakness, lack of energy or sleepiness
Other general symptoms:
- Loss of appetite
- Unexplained weight loss
- Pain or aches in your bones or joints
- Swollen abdomen
If your doctor suspects you may have leukemia, they will want to perform a thorough physical examination and talk with you about your medical history.
An accurate diagnosis of CML requires several tests. You might have any or all of these.
- Blood tests — to check the types and numbers of blood cells, check the amount of hemoglobin (protein that carries oxygen) and look at the size and shape of the cells and whether they contain granules (complete blood count and peripheral blood smear) and to see if leukemic cells are present (immunophenotyping, or flow cytometry). Sometimes CML is discovered during a routine blood test.
- Bone marrow tests — taking samples of bone marrow and a small piece of bone from your pelvis using a needle (bone marrow aspiration and biopsy) and checking them for leukemic cells.
- Chromosome tests — checking your blood or bone marrow cells for changes in chromosomes, such as missing parts of chromosomes or two chromosomes that have exchanged some DNA. These tests include cytogenetic analysis, fluorescent in situ hybridization and polymerase chain reaction.
- Imaging tests — such as chest X-ray, computed tomography (CT) scan, magnetic resonance imaging (MRI) scan or ultrasound to check whether leukemia is impacting other parts of your body.
Phases of CML
Doctors divide CML into phases based on how the disease is behaving and how it is affecting you. Knowing the phase of your disease helps your team recommend the most effective treatment.
Most people with CML are diagnosed in the chronic phase.
- They typically have few or no symptoms unless their white blood cell counts are very high.
- They have a low percentage (less than 10 percent) of immature blood cells (blasts) in their blood and bone marrow.
With targeted therapy, chronic-phase CML can be managed for many years, perhaps indefinitely, without progressing. Your blood and bone marrow essentially go back to normal and doctors can detect very little or no CML.
Accelerated-phase CML may occur after targeted therapy for CML or when a patient is first diagnosed and hasn’t yet had any treatment.
People with accelerated-phase CML may have:
- Symptoms of CML
- More blasts in their bone marrow or blood (10 to 20 percent)
- More basophils (a type of white blood cell) in their blood (more than 20 percent)
- New chromosome changes in their CML cells
Treatment for this phase includes targeted therapy, chemotherapy and bone marrow transplant.
In the blast phase, CML acts like an aggressive acute leukemia, which is why this phase may also be called the acute phase or the blast-crisis phase.
People with blast-phase CML have symptoms and have more blasts in their bone marrow or blood (more than 20 percent).
This phase is rare and typically occurs in people who had targeted therapy for chronic-phase CML, but their disease progressed. Bone marrow transplant is often recommended.
How common is CML?
About 9,000 people are diagnosed with CML each year in the U.S.
What causes CML?
Doctors do not know what causes CML.
In almost all cases, CML cells have a chromosomal abnormality known as the Philadelphia chromosome. This means parts of chromosomes 9 and 22 rearranged. Two genes called BCR and ABL fused together in chromosome 22 to make one gene called BCR-ABL. This is called Philadelphia chromosome–positive CML (PH+ CML).
- CML typically affects older people — the average age is 64 — but it can affect people of any age.
- The disease is slightly more common in males than females.
- Exposure to high levels of radiation may increase your risk. However, no link has been shown between dental or medical X-rays and CML.
Keep in mind that most people who develop CML have none of these risk factors, and most people with these risk factors do not develop the disease.