Minimally differentiated acute myeloid leukemia (MO).

Morphologic, cytochemical, immunophenotypic and cytogenetic features of AML-MO blasts and their proliferation in a soft agar cultures were studied in 18 patients. To evaluate the role of the modern techniques in differentiation of ANLL FAB types, the following patient groups were compared: AML-MO (18 cases), AML M1 (41 cases), AML M6 (25 cases) and MDS RAEB-T (3 cases). Populations of the bone marrow nonblastic cells were compared in AML MO and AML M1 to detect the presence of myelodysplastic features. AML MO showed remarkable heterogeneity of morphologic, cytochemical, immunophenotypic and cytogenetic patterns of the blast cells. These cells are not able to proliferate in agar cultures. Prognostically unfavorable karyotype changes (including rearrangements of 3q21/q26, -5/5q-, -7/7q- and complex chromosome abnormalities) were more often observed in AML MO than AML M1 and AML M2. The difference was statistically significant, Isolated bone marrow dysplasia of granulocytic or erythroid cells and twolineage dysplasia in AML MO was recorded three times more frequently than in AML M1. Trilineage bone marrow dysplasia was revealed in AML MO only. MO blast cells were associated not only with AML but also with CML BC (34%) and MDS RAEB-T (12.5%). The recognition of AML MO is essential for a complete cytologic classification of AML. All AF cases must be examined with large panel of cytochemical markers including MPO, SBB, granulocytic esterase. In addition, immunophenotyping must be performed.