Approximately one fourth of children with newly diagnosed acute lymphoblastic leukemia (ALL) have hyperdiploid (greater than 50 chromosomes) blasts and a relatively favorable prognosis. Nonetheless, a substantial proportion of these patients fail therapy. We studied 138 children (70 male, 68 female) with hyperdiploid greater than 50 ALL to assess initial clinical and cytogenetic features that might predict treatment failure. In 85 of these cases (62%), structural chromosomal abnormalities were also present; clinical and laboratory features in this group did not differ from those of the 53 cases with only numeric abnormalities. However, of the 28 failures seen at a median follow-up of 4 years, 22 occurred in cases with structural chromosomal abnormalities (P = .03 by Breslow test). In a multivariate analysis, only the presence of structural chromosomal abnormalities and male gender were independently associated with treatment failure. Structural chromosomal abnormalities in cases of ALL with greater than 50 chromosomes may define a biologically different form of leukemia characterized by increased likelihood of drug resistance.

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