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Chronic Myelogenous Leukemia

Chronic myelogenous leukemia (CML) is a slow-progressing leukemia associated with a specific genetic abnormality in the leukemia cell, called the Philadelphia chromosome. This abnormal gene is produced when genetic material called ABL is displaced from chromosome 9 and replaces the normal part of chromosome 22 next to a region called BCR. The resulting fusion gene, BCR/ABL, causes abnormal function of the ABL gene, which leads to the leukemia.

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There are three main phases of CML:

  • The disease almost always starts in the chronic phase, during which the disease is usually easy to control with treatment, and patients can lead nearly normal lives.
  • The disease may progress over a few years into the accelerated phase. When this happens, the blood counts worsen and patients can experience high fever, bone pain and painful enlargement of the spleen.
  • The blast phase of CML is a form of acute leukemia that is very difficult to treat. Two-thirds of the time it is myeloid, and is considered acute myeloid leukemia. One-third of the time, it is lymphoid (acute lymphoblastic leukemia, or ALL). Survival is usually only a matter of months once the blast phase occurs.
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Most patients with CML initially visit their doctor because of:

  • Fatigue
  • Low-grade fevers or sweats
  • Fullness in the abdomen caused by an enlarged spleen

Chronic myelogenous leukemia is generally suspected when tests reveal an elevated white blood cell count with immature "myeloid" cells in the blood.

The diagnosis is then confirmed by the presence of the Philadelphia chromosome, either by chromosome analysis, called cytogenetics, or by molecular testing for the abnormal BCR/ABL gene. A bone marrow biopsy helps determine whether the CML is in the chronic or advanced stage.

Tyrosine Kinase Inhibitors

The mainstay treatment for chronic phase CML is tyrosine kinase inhibitors (TKIs), such as imatinib (Gleevec), dasatinib (Sprycel) or nilotinib (Tasigna). TKIs are oral medications that shut down the abnormal protein produced by the BCR/ABL gene.

With TKIs, 80 percent of CML patients will have complete disappearance of the Philadelphia chromosome and restoration of normal blood counts. The life expectancy of chronic phase CML patients taking TKIs has improved from four to six years to well over a decade. In most patients, TKIs prevent conversion to the accelerated or blast phase. Dasatinib or nilotinib works for most patients who are resistant to imatinib.

Side effects of TKIs include rash, upset stomach, swelling of the eyelids, mild lowering of the blood counts and rare episodes of fluid build-up around the lungs and/or heart.

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Reviewed by health care specialists at UCSF Medical Center.