What is Chronic Myeloid Leukemia (CML)?

Leukemia is cancer that forms in your bone marrow, the soft, spongy tissue inside your bones where blood cells are produced. Your bone marrow contains immature, blood-forming stem cells that eventually develop into mature red blood cells, white blood cells, and platelets. In Chronic Myeloid Leukemia (CML), too many of your stem cells develop into abnormal, immature white blood cells (blasts). CML is "chronic" because it is slow-growing and not very aggressive. CML is "myeloid" because the blasts are abnormal granulocytes, a type of white blood cell that develops from myeloid stem cells. These abnormal, immature cells can crowd out your healthy blood cells causing conditions like anemia (low red blood cells), leukopenia (low white blood cells), and thrombocytopenia (low platelets). These abnormal cells can eventually spread through your bloodstream to your lymph nodes and other organs.

Most people develop CML because of a genetic abnormality called the Philadelphia chromosome, in which DNA is transferred between two chromosomes, usually 9 and 22. When DNA is swapped between these chromosomes, an extra-long and an extra-short chromosome result. Abnormal chromosome 22 is the extra-short chromosome, called the Philadelphia chromosome. It forms a gene called the BCR-ABL1 gene that produces an abnormal protein that causes uncontrolled growth of malignant white blood cells. CML is the least common of the four main types of leukemia, with about 9,000 new cases each year, mostly in older adults.