Microgranular promyelocytic leukemia: a multiparameter examination

Six cases of microgranular variant acute promyelocytic leukemia (M3v) were studied by use of a multiparameter approach including morphology, cytochemistry, flow cytochemistry, flow cytometry, cytogenetics, and gene rearrangement. Three of six cases demonstrated both myeloid and monocytoid associated surface markers by flow cytometry. One of six cases had strong alpha-naphthyl-butyrate esterase (alpha-NBE) activity in addition to myeloperoxidase activity. There was no correlation between percentage of positive monocytoid surface markers and intensity of cytoplasmic alpha-NBE activity. Four of six cases also had a T-cell-associated surface antigen. Further studies indicated that the T-cell markers appeared to be on the promyelocytes and that the T-B receptor gene was not rearranged. Similarly, cytogenetics studies indicated only one clonal abnormality t(15q+; 17q-). Whether these cases represent true "lineage infidelity" remains to be answered. Future important studies are needed on normal hematopoietic progenitor cells at early stages of development and childhood to study lineage-specific characteristics and to determine whether co-expression normally exists during early development.