- Intensification and continuation therapy, begins 4-5 weeks after diagnosis for "Standard Risk" and "High Risk" groups and 4-5 weeks after infant intensification in "Infant/High Risk" group. This phase of treatment continues until the completion of two years of treatment. Patients in the "Standard Risk" group will receive five anti-leukemia drugs (vincristine, prednisone, methotrexate, asparaginase, and 6-mercaptopurine). Patients in "High Risk" and "Infant/High Risk" will receive six anti-leukemia drugs (vincristine, prednisone, doxorubicin, methotrexate, asparaginase and 6-mercaptopurine).