Chronic myeloid leukemia (CML), also called chronic myelogenous leukemia, is a type of cancer affecting the blood and bone marrow.

In CML, the bone marrow − the soft, spongy center of the bone where blood cells form − produces too many white blood cells. White blood cells normally help fight infection and disease. But in CML, the white blood cells become abnormal. They begin to grow too fast and crowd out normal healthy cells.

CML occurs most often in adults, but it can occur in children and teenagers. Fewer than 200 children and teenagers (people younger than 20 years old) in the United States are diagnosed with CML each year. CML represents roughly 3 percent of childhood leukemia and about 15 percent of leukemia in adults.