Phases of Chronic Myeloid Leukemia

Chronic Myeloid Leukemia is divided into three phases: chronic, accelerated, or blast to help doctors plan treatment and predict prognosis (the chance of recovery).

  • Chronic phase – The blood and bone marrow contain less than 10% blasts. Blasts are immature white blood cells. This phase can last for several years. However, the disease can progress to accelerated or blast phases without adequate treatment. About 90% of people have chronic phase CML when diagnosed. Few people with chronic phase CML have symptoms when diagnosed, and some do not. Most symptoms go away once treatment begins.
  • Accelerated phase – There is no particular definition of accelerated phase. However, many patients with this phase of CML have 10% to 19% blasts in both the bone marrow and blood or more than 20% basophils in the peripheral blood. A basophil is a particular type of white blood cell. These cells sometimes have new cytogenetic changes and the Philadelphia chromosome because of additional DNA damage and mutations in the CML cells.
  • Blast phase also called blast crisis – In the blast phase, there are 20% or more blasts in the blood or bone marrow, and it is difficult to control the number of white blood cells. The CML cells often have additional genetic changes as well. The blast cells can look like the immature cells seen in patients with other types of leukaemia, specifically acute lymphoblastic leukaemia for about 25% of patients or acute myeloid leukaemia for most patients. Patients in the blast phase often have a fever, an enlarged spleen, weight loss, and generally feel unwell.
  • Resistant CML – Resistant CML is CML that has come back after treatment or does not respond to treatment. If the CML does recur, there will be a round of tests to know about the extent of the disease. These tests and scans are usually similar to those at the original diagnosis.

Without effective treatment, CML in the chronic phase will eventually move into the accelerated phase and then into the blast phase about 3 to 4 years after diagnosis. Patients who have more blasts or increased levels of basophils, chromosome changes in addition to the Philadelphia chromosome, high numbers of white blood cells, or a very enlarged spleen often experience the blast phase sooner.