Philadelphia chromosome–positive chronic myeloid leukemia (Ph+ CML) Ph+ CML is a type of leukemia, which is a cancer of the blood and bone marrow. Ph+ CML results when the white blood cells behave abnormally, which triggers the production of too many immature or damaged white blood cells. These abnormal leukemic white blood cells build up in the bone marrow over time, and then infiltrate the body via the bloodstream, taking over healthy white and red blood cells and platelets, leading to chronic myelogenous leukemia (CML).