Chronic Myeloid Leukemia (CML) is a type of cancer that starts in the blood-forming cells of the bone marrow and invades the blood. It is characterized by the presence of an abnormal chromosome called the Philadelphia chromosome, which leads to the production of an abnormal protein that causes the uncontrolled growth of white blood cells. CML progresses through three phases: chronic, accelerated, and blast crisis, with each phase indicating the severity of the disease.