Phases of chronic myeloid leukemia

CML is divided into 3 groups that help predict outlook. Doctors call these groups phases instead of stages. The phases are based mainly on the number of immature white blood cells - myeloblasts (“blasts”) - that are seen in the blood or bone marrow. Different groups of experts have suggested slightly different cutoffs to define the phases, but a common system (proposed by the World Health Organization) is described below.

Chronic phase

Patients in this phase typically have less than 10% blasts in their blood or bone marrow samples. These patients usually have fairly mild symptoms (if any) and usually respond to standard treatments. Most patients are diagnosed in the chronic phase.

Accelerated phase

Patients are considered to be in accelerated phase if any of the following are true:

- The bone marrow or blood samples have more than 10% but fewer that 20% blasts
- High blood basophil count (basophils making up at least 20% of the white blood cells)
- High white blood cell counts that do not go down with treatment
- Very high or very low platelet counts that are not caused by treatment
- New chromosome changes in the leukemia cells

Patients whose CML is in accelerated phase may have symptoms such as fever, poor appetite, and weight loss. CML in the accelerated phase does not respond as well to treatment as CML in the chronic phase.

Blast phase (also called acute phase or blast crisis)

Bone marrow and/or blood samples from a patient in this phase have more than 20% blasts. The blast cells often spread to tissues and organs beyond the bone marrow. These patients often have fever, poor appetite, and weight loss. At this point the CML acts much like an aggressive acute leukemia.

Not all doctors may agree with or follow these cutoff points for the different phases. If you have questions about what phase your CML is in, be sure to have your doctor explain it to you.