Acute lymphocytic leukemia is a 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. There are three main subtypes (L1, L2 and L3) which are differentiated by the appearance of the cancerous cells: L2 is characterized by larger cells, an irregular-shaped nucleus, more cytoplasm and significant variation between cells. L2 has a poorer prognosis than L1. L2 is the main form in adults (about 65%) but is less common in children (about 15%). See also Leukemia, Lymphocytic, Acute, L2