Cytogenetics and molecular genetics of childhood leukemia.

Childhood leukemia is the commonest form of childhood cancer and represents clonal proliferation of transformed hemopoietic cells as a result of genetic changes. Molecular characterization of these changes, in particular chromosomal translocations, has yielded a wealth of information on the mechanisms of leukemogenesis. These findings have also allowed the development of sensitive assays for the identification of underlying molecular defects, which is applicable to disease diagnosis and to monitor response to treatment. Genetic alterations in childhood leukemia are powerful prognostic indicators. TEL-AML1 fusion and hyperdiploidy >50 chromosomes are associated with a good prognosis in childhood acute lymphoblastic leukemia, whereas BCR-ABL fusion and MLL rearrangements are associated with a poor prognosis. Hence cytogenetic and molecular genetic classification of childhood leukemia will significantly improve the ability of clinicians to predict therapeutic response and prognosis, which paves the way for risk stratification based on clinical and genetic features. Finally, deciphering of genetic lesions in leukemia has allowed elucidation of the molecular basis of current treatment, as typified by the success of all-trans retinoic treatment in acute promyelocytic leukemia, and has identified targets for novel therapeutic approaches. It is envisaged that efforts in characterization of molecular defects in childhood leukemia will ultimately be translated into better clinical outcome for patients. Copyright 1999 John Wiley & Sons, Ltd.