Updated on April 9, 2025.
Chronic myeloid leukemia (CML) is a type of cancer that begins in the bone marrow, with mutations that affect the normal production and function of white blood cells. This cancer is also known as chronic myelogenous leukemia.
CML occurs when blood-forming cells in the bone marrow (myeloid cells) undergo genetic mutations. These mutations create abnormal white blood cells that grow and divide at a faster-than-normal rate.
While this disease is typically slow to progress, it does progress, and over time large numbers of abnormal white blood cells can build up in the bone marrow and blood. High numbers of CML cells will crowd out healthy cells, and can cause a variety of symptoms and complications, including anemia, bleeding, infections, an enlarged spleen, and bone pain. CML can also change over time, growing faster and becoming more difficult to treat.
Drugs called TKIs are the main treatment for most cases
CML is not considered curable, but it is manageable. Most people with CML are diagnosed in the early phase of the disease, called the chronic phase. This phase is manageable with treatment, and many people in the chronic phase of the disease have a normal or near-normal life expectancy.
CML in the early phase of the disease is most often treated with oral medications called TKIs. “TKI” refers to “tyrosine kinase inhibitor.” These are targeted therapies that interrupt the lifecycle of CML cells by blocking a protein called tyrosine kinase. Blocking this protein prevents new CML cells from forming. If the cancer responds to treatment, this will lower the number of CML cells in the body. A person will need to continue to take a TKI to keep CML under control, and treatment is a lifelong process.
Tests to measure and monitor treatment response
Response to treatment will be measured with lab tests that examine blood and bone marrow. The goal is to achieve and maintain normal counts of healthy blood cells and very low numbers of CML cells.
Your healthcare team will be looking for:
- Hematologic response. This refers to a complete blood cell count that measures red blood cells, white blood cells, and platelets. Tests will also look for immature cells and check the size of the spleen.
- Cytogenetic response. This test checks a sample of bone marrow. It looks for the percentage of cells in the bone marrow that contain the Philadelphia chromosome or Ph chromosome, a genetic abnormality found in CML cells.
- Molecular response. This is measured using a polymerase chain reaction (PCR) test. These tests check for small amounts of genetic material found in CML cells from blood and bone marrow samples.
Your healthcare provider can explain in more detail what these tests measure and what your tests results mean.
These tests are typically given at least every three months during the first year a person is treating CML. The schedule and frequency of tests can vary from person to person, and it may change over time depending on the response to treatment and other factors.
A healthcare team will also monitor for side effects—like other cancer treatments, TKIs come with a risk of side effects, including nausea, diarrhea, skin rash, fluid buildup, and lowered blood cell counts. This is a topic that should be discussed prior to starting any cancer treatment.
If CML is not responding to treatment with TKIs or if a TKI is causing unmanageable side effects, a healthcare team may change the dosage or switch to a different drug or combination of drugs.
Other treatment options
TKIs are not the only therapy used in the treatment of CML. In some cases, treatment may include chemotherapy and therapies to lower very high white blood cell counts. An allogeneic stem cell transplant has the potential to cure some cases of CML, but is only recommended in select cases—it requires high doses of chemotherapy (and sometimes radiation) to eliminate leukemia cells and comes with a high risk of side effects. Allogeneic stem cell transplant has become less common as TKI treatments have become available.
For information on treatment options and monitoring response to treatment, a healthcare team will be your best source of information.
