Near-tetraploidy in childhood B-cell precursor acute lymphoblastic leukemia is a highly specific feature of ETV6/RUNX1-positive leukemic cases.

Near-tetraploidy (82-94 chromosomes) makes up fewer than 1% of childhood acute lymphoblastic leukemia (ALL) cases and has been reportedly associated with a possibly poorer prognosis compared with other ploidy groups. We analyzed 783 patients enrolled in the ALL-BFM-Austria 86, -90, -95, -99/2000 and Interfant-Austria 99 trials in order to assess its incidence, biological characteristics, and prognostic relevance. Twelve of 783 patients (1.5%) had a near-tetraploid ALL. Fluorescence in situ hybridization revealed that eight of the nine B-cell precursor (BCP) cases and none of the three T-cell ALL cases had an ETV6/RUNX1 rearrangement. After a median follow-up of 11.4 years, none of the patients has relapsed or died. Thus, near-tetraploidy appears to be a specific feature of ETV6/RUNX1+ BCP ALL cases that in turn may explain its excellent outcome.