Chronic Myeloid Leukemia (CML): What to Know

Chronic myeloid leukemia, or CML, is a cancer of the blood and bone marrow. Bone marrow is the spongy tissue inside bones where blood cells are made.

In almost all CML, a piece of chromosome 9 swaps places with a piece of chromosome 22. The result is called the Philadelphia chromosome. It creates a new fused gene, BCR::ABL1. That gene makes a protein called a tyrosine kinase, and the protein tells the marrow to make far too many white blood cells. The change is not inherited, and you cannot pass it to your children.

Some people have no symptoms at all, and CML is found on a routine blood test. Others feel very tired, lose weight without trying, run a fever, or have drenching night sweats.

Testing usually includes blood counts, a bone marrow sample, chromosome testing for the Philadelphia chromosome, and a molecular test for BCR::ABL1.

Ask which tests are done and which are still pending. The molecular test matters most. It gives a starting number that later tests are measured against.

CML is described in three phases. They are based on the share of very young cells, called blasts, in the blood or marrow:

• Chronic phase. Fewer than 10% blasts. Most people are diagnosed here.
• Accelerated phase. Between 10% and 19% blasts.
• Blastic phase. 20% or more blasts. This is sometimes called blast crisis, and it can come with fever, fatigue, and a swollen spleen.

The phase guides treatment. So does how well the disease responds over the first months.

Most treatment uses a daily pill called a tyrosine kinase inhibitor, or TKI. It blocks the protein the fused gene makes. Approved TKIs for CML include imatinib, dasatinib, nilotinib, bosutinib, and asciminib. Which one fits you depends on your phase, your other health conditions, and side effects.

Your team will recheck BCR::ABL1 in your blood on a schedule to see how well the drug is working. A stem cell transplant or a different drug may be discussed if the disease resists treatment or reaches an advanced phase.

Do not stop or skip a TKI on your own, even if you feel well. Some people can try stopping later, but only under close monitoring arranged by a specialist. Tell your team about every other medicine you take, and mention if you have had weight-loss surgery, because it can reduce how much of the pill your body absorbs.

• Stage or spread does not always mean the same thing in blood cancers as it does in solid tumors.
• A slow-growing blood cancer is not always harmless; it still needs follow-up.
• A fast-growing blood cancer is not automatically hopeless; some respond strongly to treatment.
• A remission still requires monitoring.
• Supportive care, infection prevention, transfusions, and symptom control are part of treatment, not extras.

• What exact subtype do I have?
• Is it fast-growing or slow-growing?
• What genetic, chromosome, or molecular results matter?
• Do I need treatment now, or is observation reasonable?
• What symptoms or lab changes would make us act sooner?
• Is a clinical trial worth discussing?

CML and its treatment can lower the blood cells that fight infection. An infection can turn serious quickly.

• Call 911 or go to an emergency department if you have a fever of 100.4°F (38°C) or higher, the threshold CDC gives for infection during cancer treatment, with shaking chills, if you feel confused or very short of breath, or if you have bleeding that will not stop.
• Call your care team immediately, at any hour, if you have a fever of 100.4°F (38°C) or higher on its own, with no other symptom at all. While you are on a tyrosine kinase inhibitor your white cells can be low, and a temperature is a medical emergency. If nobody answers quickly, go to an emergency department and tell them you are being treated for leukemia.
• Call your care team the same day if you have new bruising or tiny red spots on your skin, blood in your urine or stool, or sudden severe pain in the upper left side of your belly, where the spleen sits.
• Call your care team within a day or two if you have new or worsening tiredness, drenching night sweats, unexplained weight loss, or side effects from your pill that are making it hard to keep taking it. Ask what to change rather than stopping on your own.

Start with Leukemia, Lymphoma, Multiple Myeloma, Blood and Marrow Stem Cell Transplant, and CAR T-Cell Therapy.

• National Cancer Institute — Chronic Myeloid Leukemia Treatment (PDQ) Patient Version
• National Cancer Institute — Infection and Neutropenia During Cancer Treatment
• MedlinePlus — Chronic Myeloid Leukemia