A 61-year-old woman presented with pancytopenia, hemoglobin 100 g/L, neutrophils 0.77 × 10⁹/L, and platelets 50 × 10⁹/L. Blood film showed a leukoerythroblastic picture with cytoplasmic vacuolated blasts. Marrow aspirate was dry tap, but touch preparations of the biopsy demonstrated sheets of blasts with Burkitt-like morphology including basophilic cytoplasm, variable numbers of nucleoli, and cytoplasmic vacuolations (panel A; original magnification ×100; oil immersion). Flow immunophenotyping of the peripheral blood showed 13% blasts, which were CD19⁺/CD10⁺/Tdt⁺/CD22⁺/HLA⁻DR⁺/partial CD20⁺, but were negative for CD45⁻/CD34⁻. Biopsy was hypercellular with blasts having irregular nuclear-contour (panel B; original magnification ×40; hematoxylin and eosin stain). Immunohistochemistry illustrated the blasts were CD19⁺/CD10⁺/partial CD20⁺/CD79⁺/PAX5⁺/BCL6⁺/Tdt⁺/Ki-67⁺ (>90%)/P53⁺/C-MYC⁺ (60% to 70%; panel C; original magnification ×40; C-MYC stain). These findings were consistent with B acute lymphoblastic leukemia (B-ALL). Chromosome analysis showed near-triploidy with 66 chromosomes (panel D), confirmed by fluorescence in situ hybridization studies to be present in 14% of cells. The patient was treated with a hyper–cyclophosphamide, vincristine, doxorubicin, and dexamethasone regimen but died with relapse 11 months after initial diagnosis.

Near-triploidy is a rare chromosomal abnormality in adult B-ALL with a 93% TP53 mutation rate, thought to arise from doubling of a masked hypodiploid clone. It has been suggested that near-triploidy, with or without a hypodipoid clone, should be included in the B-ALL with hypodiploidy with poor prognosis and should not be confused with B-ALL with hyperdiploidy (>50 and usually <66 chromosomes) with favorable prognosis.