ALL therapy. Classic phases of ALL therapy. The approach is similar across cooperative groups; however, the nomenclature is different. (A) Names of phases used by some cooperative groups, including the Children’s Oncology Group (COG). (B) Names of phases used by other groups, including the Berlin-Frankfurt-Muenster (BFM). The first phase of therapy (induction or induction 1A) consists of 3 to 4 agents and lasts ∼4 weeks, with the goal of achieving remission. This is followed by 3 to 4 months of therapy to consolidate remission. These blocks classically include 1 to 2 months of multiagent chemotherapy with CNS prophylaxis and 2 months of further intensification using a variety of methotrexate-based regimens. The blocks are termed consolidation and interim maintenance (IM) by the COG and induction IB and protocol M by the BFM. The third phase of therapy is intensification, termed delayed intensification (DI) by the COG and protocol II by the BFM. Intensification essentially repeats the therapy used in the first 3 months, with substitution of some agents with drugs in the same class. Finally, the fourth phase of therapy is termed maintenance and consists of low-intensity chemotherapy lasting for 1 to 3 years. Some protocols include a second IM and/or a second DI after DI/protocol II and before maintenance.