Prognostic implication and characterization of the blast cell population in the myelodysplastic syndrome.

The bone marrow smears of 18 confirmed cases of MDS were analyzed carefully for the presence of "hypergranular type III blasts", defined as more than 20 fine azurophil primary granules per cells. The concordance was close to 80% among 5 observers. Thirty-nine percent (7 cases) were reclassified as RAEB-t rather than RAEB. The presence of these hypergranular blasts was not suggestive of increased differentiation but rather leukemic cells. The reassignment of cases altered the median survival for the various subcategories, providing a clearer separation with the introduction of type III blasts than without utilizing these cells which were separated from the promyelocyte family. The introduction of this new blast cell definition in a larger series of patients is recommended to confirm these preliminary observations.