Leukemia - Chronic Myeloid - CML: Phases

Approved by the Cancer.Net Editorial Board, 11/2016

ON THIS PAGE: You will learn about how doctors describe the growth or spread of CML. This is called the phase. To see other pages, use the menu.

To help doctors plan treatment and predict prognosis, which is the chance of recovery, CML is divided into 3 different phases: chronic, accelerated, or blast.

  • 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, without effective treatment, the disease can progress to the accelerated or blast phases (see below). About 90% of people have chronic phase CML when they are diagnosed. Some people with chronic phase CML have symptoms when they are diagnosed and some do not. Most symptoms go away once treatment begins.

  • Accelerated phase. There is no single definition of accelerated phase. However, most patients with this phase of CML have 10% to 19% blasts in both the blood and bone marrow or more than 20% basophils in the peripheral blood. A basophil is a special type of white blood cell. These cells sometimes have new cytogenetic changes in addition to 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 acute lymphoblastic leukemia for about 25% of patients or acute myeloid leukemia for most patients. Patients in 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. This is different from CML that has developed a resistance to treatment, which means that a specific treatment no longer works. If the CML does return, there will be another round of tests to learn about the extent of the disease. These tests and scans are often similar to those done at the time of the original diagnosis.

Without effective treatment, CML in chronic phase will eventually move into accelerated phase at first and then into blast phase in about 6 to 8 years after diagnosis. Patients who have more blasts or an increased number of basophils, chromosome changes in addition to the Philadelphia chromosome, high numbers of white blood cells, or a very enlarged spleen often experience blast phase sooner.

Information about the phase of CML will help the doctor recommend a specific treatment plan. The next section in this guide is Treatment Options. Or, use the menu to choose another section to continue reading this guide.