Most types of cancer are grouped in stages. Stages tell the size of the tumor and how far the cancer has spread. But chronic myeloid leukemia (CML) is different. It rarely causes tumors. And because it's in your bone marrow and blood, the leukemia cells are always moving around the body.

Instead of stages, CML is described in phases. The phases note how many immature white blood cells (called blasts) are in the blood or bone marrow. The phase of CML is one of the most important things to know when deciding how to treat this type of leukemia.

There are 3 phases of CML:

• Chronic phase. During this phase, you have fewer than 10% immature white blood cells, called blasts, in your blood or bone marrow. If there are symptoms, they're mild and get better with treatment. Most people diagnosed with CML are in this phase. It progresses slowly. People can stay in this chronic phase for many years.
• Accelerated phase. During this phase, you have one or more of these:
  • 10% or more, but fewer than 20% blasts
  • 20% or more of a type of white blood cell called basophils
  • A very low platelet count (these are blood cells that prevent bleeding by helping the blood to clot)
  • The number of blast cells plus the number of promyelocytes (an immature myeloid cell) make up 30% or more of your blood
  • New gene changes in the leukemia cells that have the Philadelphia chromosome
• You may have symptoms such as a fever, low appetite, enlarged spleen, and weight loss. Symptoms and blood counts may not respond as well to treatment. This phase is more aggressive.
• Blast phase (blast crisis). During this phase, you have 20% or more blasts in your blood, bone marrow, or both. These blast cells often spread outside the bone marrow. Blood counts are not normal. You may have symptoms such as severe tiredness (fatigue), fever, loss of appetite, bleeding, shortness of breath, and an enlarged spleen. This phase means the cancer is growing quickly and is more aggressive.

Not all doctors agree on these cutoff points for the 3 phases. Talk with your doctor about what phase your CML is and why.

Once the phase of your CML is known, your doctor will talk with you about what it means for your treatment. Be sure to ask any questions or talk about your concerns.