Molecular Cytogenetics in Childhood Leukemia

In the last decade molecular cytogenetics, or fluorescence in situ hybridization (FISH), has become an important complementary procedure to routine chromosomal analysis. The most significant consequence from cytogenetic studies in childhood leukemia has been the association of specific chromosomal abnormalities with different patient subgroups, particularly in relation to prognosis. In childhood acute myeloid leukemia (AML), the rearrangements t(8;21)(q22;q22), t(15;17)(q22;q12), and inv(16)(p13q22) are associated with a good outcome. Conversely, deletions of the long arm of chromosome 5, monosomy 5 or 7, in association with a complex karyotype, are related to a poor prognosis (1 ). Karyotypes with a favorable outcome in childhood acute lymphoblastic leukemia (ALL) include high hyperdiploidy (51–65 chromosomes) and the translocation, t(12;21)(p13;q22). The Philadelphia translocation, t(9;22)(q34;q11), rearrangements involving the MLL gene and near haploidy (23–29 chromosomes) are associated with a short overall survival (2 ). Metaphase and interphase FISH are increasingly being used to screen routinely for such chromosomal abnormalities in childhood leukemia. Metaphase FISH also plays a role in the identification of new nonrandom chromosomal changes of prognostic significance.