Contemporary treatments have resulted in 5-year event-free survival rates (EFS) of approximately 75% to 80% for childhood acute lymphoblastic leukemia (ALL). Relapses of ALL in children were more often in HR-ALL but also in very few non-HR-ALL. Thus current clinical study of ALL has focused on improving the outcome of a few subtypes of HR-ALL. Infants with ALL have a particularly high risk of treatment failure. Infant ALL Interfant-99 study found that MLL rearrangement, age younger than 6 months, poor response to a prednisone prophase and high WBC count were strong independent predictive factors for poor prognosis in infants with ALL. Treatments with hybrid protocol, including both lymphoid- and myeloid-directed treatment elements, also contain HD-MTX and high dose Ara-C ( HD-Ara-C) , will further improve the outcome for infant ALL. Children Philadelphia chromosome positive ALL ( Ph + ALL) was associated with a high relapse rate when treated with chemotherapy alone. The Children' s Oncology Group (COG) AALL0031 trial showed that the addition of tyrosine kinase inhibitors (TKIs) imatinib to intensive chemotherapy resulted in 3-year EFS more than historical control treated with chemotherapy alone. These findings create a new paradigm for integrating molecularly targeted agents with intensified chemotherapy. Children with T-ALL have had a worse outcome than with the precursor B-cell ALL previously. With more intensified chemotherapy , outcomes for children T-ALL were improved, approaching those for the precursor B-cell ALL. Recently, COG decided to treat children with T-cell ALL with separate protocols different from those for the precursor B-cell ALL, and the protocols of BFM for children with T-ALL have been the same as those of the precursor B-cell ALL. Early precursor T-cell ALL, a novel subtype of T-cell ALL, was identified by gene expression profiling, flow cytometry, and single nucleotide polymorphism array analyses. ETP-ALL, identified in 13% of T-cell ALL cases, is characterized by a distinctive immunophenotype ( CD1 a and CD8 negativity, with weak expression of CD5 and co-expression of stem cell or myeloid markers). A retrospective analysis suggested that ETP-ALL had a poor prognosis. The advent of high-resolution genome-wide analyses has provided new insights into leu-kemogenesis and identified many novel subtypes of leukemia. Ph-like ALL ( BCR-ABL1 -like ALL) patients lack a previously identified chromosomal rearrangement, but exhibit a gene-expression profile highly similar to that of Ph + ALL, and often have deletion/mutation of IKZF1 , CRLF2 rearrangments and JAK1/2sequence mutations which are also common in Ph + ALL. The prognosis of Ph-like ALL is poor. Development of new agents targeted to leukemogenic pathways will promise to further improve the outcome of children ALL.
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