Isochromosome 17q in childhood acute lymphoblastic leukemia: an adverse cytogenetic feature in association with hyperdiploidy?

Isochromosome 17q is associated with the blastic phase of Philadelphia chromosome-positive chronic myeloid leukemia, but its significance in acute lymphoblastic leukemia (ALL) is unknown. We studied 469 consecutive cases of newly diagnosed ALL with completely banded leukemic cell chromosomes, identifying eight that had the isochromosome. The presenting leukocyte counts of these patients ranged from 1.7 to 130.2 x 10(9)/L (median 7 x 10(9)/L). The morphologic classification of their blast cells was L1 in six cases and L2 in the others; the majority of cases had the common ALL phenotype, whereas two were pre-B. Strikingly, hyperdiploidy greater than 50 chromosomes, a favorable prognostic feature in ALL, characterized all but one of the cases with i(17q), compared with 113 of 461 cases lacking the isochromosome (p less than 0.001). Only four patients, three with relatively brief follow-up times (1, 2, and 8 months), are still in remission. All of the eight previously reported cases of ALL with the i(17q) have failed treatment. These findings suggest that the i(17q) exerts an adverse influence on treatment outcome in ALL, even in hyperdiploid cases with greater than 50 chromosomes.