NCI: The most frequent type of acute lymphoblastic leukemia. Approximately 75% of cases occur in children under six years of age. This is a good prognosis leukemia. In the pediatric age group the complete remission rate is approximately 95% and the disease free survival rate is 70%. Approximately 80% of children appear to be cured. In the adult age group the complete remission rate is 60-85%. (WHO, 2001),NCI: An aggressive (fast-growing) type of leukemia (blood cancer) in which too many B-cell lymphoblasts (immature white blood cells) are found in the bone marrow and blood. It is the most common type of acute lymphoblastic leukemia (ALL).