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Chronic Myeloid Leukemia

What is Chronic Myeloid Leukemia?

Chronic myeloid leukemia (CML), also called chronic myelogenous leukemia, is a type of cancer affecting the blood and bone marrow.

In CML, the bone marrow − the soft, spongy center of the bone where blood cells form − produces too many white blood cells. White blood cells normally help fight infection and disease. But in CML, the white blood cells become abnormal. They begin to grow too fast and crowd out normal healthy cells.

CML occurs most often in adults, but it can occur in children and teenagers. Fewer than 200 children and teenagers (people younger than 20 years old) in the United States are diagnosed with CML each year. CML represents roughly 3 percent of childhood leukemia and about 15 percent of leukemia in adults.

Key Terms for Chronic Myeloid Leukemia

Below are some terms to know as you learn more about chronic myeloid leukemia:

Bone Marrow

The soft, spongy center of bones where blood cells are formed.

Blood Stem and Progenitor Cells

Immature cells in the bone marrow that eventually become different types of mature blood cells. CML results from a mutation, or change, in the blood stem and progenitor cells.

White Blood Cells

Sometimes called leukocytes. Cells that are responsible for fighting infection and disease in the body. There are two categories of white blood cells – myeloid (such as granulocytes and monocytes) and lymphoid (such as B- and T-lymphocytes). CML involves the myeloid cells.

Red Blood Cells

Cells that carry oxygen to the body’s tissues.


Blood cell fragments that help with clotting

Chronic Myeloid Leukemia Causes

Chronic myeloid leukemia is caused by a specific mutation, or change, in certain genes.

In CML, a gene called BCR and a gene called ABL1 rearrange and join together, resulting in the mutant gene BCR-ABL1, also known as the Philadelphia chromosome (Ph). The Ph chromosome is found in more than 95 percent of CML cases. Blood cells with the Ph mutation grow much faster than normal cells. The mutant cells eventually crowd out healthy, normal cells and take over the blood system.

No one knows why some blood cells acquire the Ph mutation. The mutation is not hereditary, and cannot be passed from parent to child.

Chronic Myeloid Leukemia Symptoms

The early symptoms of chronic myeloid leukemia occur as cancerous cells fill up the spleen and bone marrow and crowd out normal blood cells. This results in high white blood cell counts and low red blood cell and platelet counts. Symptoms develop gradually and may include:

  • Fever
  • Fatigue and weakness
  • Shortness of breath
  • Looking pale 
  • Excessive bruising or bleeding
  • Night sweats
  • Aches and pains in the bones
  • Pain or swelling on the left side of the belly due to an enlarged spleen

Chronic Myeloid Leukemia Diagnosis

If the doctor suspects leukemia, the first step is to do a physical exam and blood tests. Blood tests will show how many white blood cells, red blood cells and platelets are in the blood. The blood cells are also examined under a microscope to find abnormal cells and the presence of leukemia.

In addition, a doctor might perform a bone marrow aspiration and biopsy. This involves inserting a needle into a large bone such as the hip bone to remove a small piece of bone marrow or fluid from the marrow to check for abnormal cells.

Other tests can be done to better understand the extent of your child’s disease, to treat it more effectively, and to see how the disease is responding to treatment.
Your doctor can explain these tests to you in more detail.

Chronic Myeloid Leukemia Treatment

Treatment begins as soon as possible after chronic myeloid leukemia is found. Doctors will treat any associated symptoms, such as fever and infections, anemia, or risk of bleeding.

Treatment for CML may include medicines called tyrosine kinase inhibitors (TKI). These drugs are taken by mouth every day, and often work very well and have few side effects.

A drug called hydroxyurea may be used at first, along with TKI therapy, to reduce the number of white blood cells in the bloodstream. After a time, the hydroxyurea is stopped and the TKI therapy continues. TKI therapy clears out CML cells and allows normal cells to fill up the marrow and blood system. Patients can stay on TKI therapy indefinitely, but are checked regularly for side effects and to confirm that there are no CML cells remaining.

Watching how your child responds to medicines is a key part of CML treatment. Doctors will test your child’s blood and/or bone marrow at certain times to track response to therapy and to help guide long-term management. When disease is no longer detected, your child is considered “in remission.” Many patients remain in remission on TKI therapy for many years.

If a child’s CML returns after a period of remission, switching to a different TKI medication can often put the CML back into remission.

Even with treatment, CML can sometimes progress to more aggressive forms of the disease. There are three “phases” of CML. They are defined by the number of immature blasts (white blood cells) involved.

  • Chronic phase, which is the most common, is characterized by fewer than 10 percent blasts in the blood. This phase is typically managed with drugs that target the BCR-ABL1 protein; the disease can remain in this phase for years.
  • Accelerated phase is characterized by up to 30 percent blasts in the blood. It is often managed with drug treatment, although your child’s doctor may recommend a stem cell transplant if there is no improvement.
  • Blast phase, which involves more than 30 percent blasts in the blood, is treated more aggressively, often with chemotherapy and a bone marrow transplant.

Treatment with stem cell transplant (also called a bone marrow transplant) involves taking healthy stem cells from a donor and transplanting them into your child’s bloodstream. The healthy stem cells make their way to the child’s bone marrow and start producing normal white blood cells, red blood cells and platelets.

If your child needs a bone marrow transplant, family members may be tested to see who might be a suitable bone marrow donor.

Stem cell transplants are challenging procedures for patients, but can provide long-term cure. Stem cell transplant specialists at Cincinnati Children’s use the latest proven approaches to improve the effectiveness and safety of stem cell transplantation. Stem cell transplant most often succeeds, but not always. Sometimes the CML stem cells may survive and re-emerge. A child may receive TKI therapy after stem cell transplant to lower the risk of future relapse.

Chronic Myeloid Leukemia Outlook

Survival rates and quality of life for patients with chronic myeloid leukemia have improved dramatically, due to more effective medicines and better methods for monitoring treatment response. Overall, life expectancy for a patient diagnosed with CML today is nearly that of the general population.

Recent studies have shown that some patients over the age of 18 who have had continuous years without evidence of CML can stop TKI therapy and remain free of disease. TKI therapy should only be stopped after talking with a doctor who specializes in treating CML.

Research has focused on developing newer and even more effective TKI drugs and gaining a better understanding of how the disease progresses. Better drug treatments have improved the ability to achieve and maintain remission. If a bone marrow transplant becomes necessary, advances in stem cell transplantation have increased the chances of long-term cures. Children who have had CML must have consistent follow-up care for the rest of their lives. This ensures that doctors can help with any side effects from treatment, and enables them to see if there are any signs of the leukemia returning, so that they can intervene quickly.

Last Updated 07/2021

Reviewed By Michelle West, RN

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