Ambiguous patterns in cellular differentiation in a case of "M3 variant" leukemia

We report a case of acute non lymphoblastic leukemia in which clinical and cytological patterns corresponded closely to the M3 variant as defined in the FAB classification, although we did not find the characteristic t (15; 17) chromosomal translocation. However, cytochemistry, DNA content studies and immunophenotyping showed unusual patterns suggesting a monocytic differentiation of most of the blast cells, while a smaller population of blasts showed in contrast typical markers of granulocytic lineage.