Chronic myelogenous leukemia is a malignant cancer of the bone marrow that causes rapid growth of the blood forming cells (known as myeloid precursors) in the bone marrow, peripheral blood, and body tissues.

occurs in middle-aged people and children and is associated with a chromosome abnormality called the Philadelphia chromosome. Chronic myelogenous leukemia is characterized by a chronic phase that can last for months or years. The disease may have few or no symptoms during the chronic phase. Eventually, patients progress from the chronic phase to a more dangerous "accerated phase," during which the leukemia cells grow more quickly.