•The treatment of childhood ALL, with the exception of B-cell ALL, has 5 components: induction, consolidation, interim maintenance, delayed intensification, and maintenance. The goal of induction is to achieve remission or <5% blasts in the bone marrow. Induction therapy generally consists of 3-4 drugs, which may include a glucocorticoid, a vincristine, an asparaginase, and possibly an anthracycline. This type of therapy induces complete remission in more than 98% of patients.

•Consolidation (ie, intensification) therapy is given soon after remission is achieved to further reduce the leukemic cell burden before the emergence of drug resistance and relapse in sanctuary sites (eg, testes, CNS). In this phase of therapy, the drugs given at doses higher than those used during induction, or the patient is given different drugs (eg, high-dose MTX and 6-mercaptopurine (6-MP), epipodophyllotoxins with cytarabine, or multiagent combination therapy). Consolidation therapy, first used successfully to treat patients with high-risk disease, also appears to improve the long-term survival of patients with standard-risk disease. The addition of intensive reinduction therapy (administered soon after remission is achieved) is similarly beneficial for patients in both risk groups.

•In interim maintenance, oral medications are administered to maintain remission and allow the bone marrow to recover. This occurs for 4 weeks and is followed by delayed intensification, which is aimed at treating any remaining resistant leukemia cells.

•The last phase of treatment is maintenance. This consists of LPs with intrathecal MTX every 3 months, monthly vincristine, daily 6-MP, and weekly MTX.

•Duration of therapy:

•Whereas B-cell ALL is treated with a 2- to 8-month course of intensive therapy, achieving acceptable cure rates for patients with B-precursor and T-cell ALL requires approximately 2-2.5 years of continuation therapy. Attempts to reduce this time result in high relapse rates after therapy is stopped.

•Most contemporary protocols include a continuation phase based on weekly parenterally administered MTX given with daily, orally administered 6-MP interrupted by monthly pulses of vincristine and a glucocorticoid. Although these pulses improve outcomes, they are associated with avascular necrosis of the bone. Patients with high-risk ALL also may benefit from intensified continuation therapy that includes the rotational use of drug pairs.