Overview

Leukemia is a cancer of the blood. Leukemia begins when normal blood cells change and grow uncontrollably. Chronic myeloid leukemia (CML) is a cancer of the blood-producing cells of the bone marrow (the spongy, red tissue in the inner part of the large bones) that primarily results in an increase in the number of white blood cells (cells that normally fight infection). CML is also sometimes called chronic granulocytic, chronic myelocytic, or chronic myelogenous leukemia. CML makes up about 9% of all new cases of leukemia.

People with CML have an acquired genetic abnormality or mutation in their bone marrow cells, in which part of one chromosome (a long strand of genes) breaks off and reattaches to another chromosome. This type of genetic exchange is called a translocation. In CML, part of chromosome 9 breaks off and fuses to a section of chromosome 22, resulting in what is called the Philadelphia chromosome or Ph chromosome. The translocation causes two genes called BCR and ABL to fuse into one gene called BCR-ABL. This mutation is found only in the blood-forming cells, not in other organs of the body, and is not inherited. Therefore, there is no concern about an increased risk to other family members.

The BCR-ABL gene causes myeloid cells to produce an abnormal enzyme that allows white blood cells to grow out of control. Ordinarily, the number of white blood cells is tightly controlled by the body—more white blood cells are produced during infections or times of stress, but then return to normal when the infection is cured. In CML, the abnormal BCR-ABL enzyme is like a switch that is stuck in the “on” position—it keeps stimulating the white blood cells to grow. In addition to the elevated white blood cell count, the number of blood platelets (cells that help the blood to clot) often increase, and the number of red blood cells, which carry oxygen, may decrease.

Statistics

In 2009, an estimated 5,050 people of all ages (2,930 males and 2,120 females) in the United States will be diagnosed with CML. Most of these will be adults; CML is rare in children. It is estimated that 470 deaths (220 males and 250 females) will occur.

The five-year relative survival rate (the percentage of people who survive at least five years after the cancer is detected, excluding those who die from other diseases) for people with CML depends on the phase of the disease, other biologic characteristics of the CML, and the response of the disease to treatment.

Cancer survival statistics should be interpreted with caution. These estimates are based on data from thousands of cases of this type of cancer in the United States each year, but the actual risk for a particular individual may differ. It is not possible to tell a person how long he or she will live with CML. Because survival statistics are measured in five-year intervals, they may not represent recent advances made in the treatment or diagnosis of this cancer. This statement is particularly true of CML, because major improvements in treatment have occurred during the past decade.

Statistics adapted from the American Cancer Society's publication, Cancer Facts and Figures 2009.

Find out more about basic cancer terms used in this section.