Acute lymphocytic leukemia is a relatively aggressive cancer of the white blood cells. Precursors to white blood cells are called blasts and are made by the bone marrow but in ALL the blasts are abnormal and do not develop into lymphocytes. Instead, the abnormal blasts or leukemic cells multiply rapidly and reduce the level of other types of blood cells such as red blood cells and platelets. The Philadelphia negative form of the condition is not associated with a genetic mutation. It is distinguished from the positive form by the clinical course which is initially the same but progresses to eventual bone marrow failure without a distinct increase in blast cells. Other differences include poor response to chemotherapy, lower white blood cell counts, greater monocytosis, less basophilia, lower bone marrow myeloid to erythroid ratio and increased likelihood of developing thrombocytopenia. Philadelphia negative patients also tend to be older and median survival rates tend to be poorer. See also Leukemia, Myeloid, Philadelphia-Negative