About 4,570 new cases of CML will be diagnosed in the US this year. The median age at diagnosis is 53, and the disease is slightly more common in men than women. Researchers have noticed an increasing proportion of younger people with CML in recent years.
CML arises when a genetic mutation called the Philadelphia chromosome occurs in the blood cells. This abnormal chromosome forms a protein (called bcr/abl) that is the hallmark of the disease. (To learn more about the Philadelphia chromosome, visit the section on CML classification.)
Patients with CML typically have elevated white blood cell counts and may have low numbers of red cells (a condition called anemia) as well as elevated levels of platelets. Cells that contain the Philadelphia chromosome eventually accumulate in large numbers in the bone marrow.
Chronic leukemias often develop gradually, and symptoms -- such as anemia, infections, and bruising and bleeding -- may not appear for several years. Doctors classify CML into three phases (chronic, accelerated, and blastic), which are usually defined by the percentage of immature cells, or blasts, in the bone marrow, as well as other features.
