Near-haploid and low-hypodiploid acute lymphoblastic leukemia: two distinct subtypes with consistently poor prognosis.

Hypodiploidy <40 chromosomes is an uncommon genetic feature of acute lymphoblastic leukemia (ALL) in both children and adults. It has long been clear by cytogenetic analyses, and recently confirmed by mutational profiling, that these cases may be further subdivided into 2 subtypes: near-haploid ALL with 24 to 30 chromosomes and low-hypodiploid ALL with 31 to 39 chromosomes. Both groups are associated with a very poor prognosis, and these patients are among those who could benefit most from novel treatments.