White blood cells defend the body against infection. Blood cells grow in the bone marrow and are supposed to be fully-grown when they enter the bloodstream. Leukemia causes white blood cells to lose their ability to fully mature. Immature cells take over the marrow. When this happens, the bone marrow cannot make enough of the other cells found in blood, like red blood cells, normal white blood cells, and platelets that the body needs.
Initial symptoms are vague.
Usually the patient does not feel very well. The first phase of treatment is to kill as many of the leukemia cells as possible and put the patient into remission. Once in remission and there are no signs of leukemia, the second phase of treatment begins. This phase may last for several years. Less intense and less frequent chemotherapy is given during this time to kill any remaining leukemia cells.