Safety in numbers: Hyperdiploidy and prognosis

Abstract

In this issue of Blood, Dastugue and colleagues report their findings examining the impact of hyperdiploidy on the outcome of children with B-cell acute lymphoblastic leukemia (ALL). Since the 1980s, it has been appreciated that 25% to 30% of B-cell ALL cases have a “high” hyperdiploid karyotype (generally defined as .50-67 chromosomes) and that this subset has an unusually good prognosis (reviewed by Paulsson and Johansson1). This feature has been used routinely to stratify patients into treatment groups. However, in spite of major progress understanding other biological subtypes of ALL, the underlying transforming pathways that define this major subgroup and those that account for the good response to therapy remain largely unknown. Moreover, controversy exists on whether the driver in both cases is the gain of specific chromosomes or whether it is due to the overall gain in chromosome number. Dastugue et al report that the best indicator of overall prognosis is ploidy assessed by karyotype and that prognosis is improved at higher modal chromosome numbers.2