Morphologic properties of neoplastic mast cells: delineation of stages of maturation and implication for cytological grading of mastocytosis

In the present study, cytological properties of bone marrow mast cells (MC) were analyzed and correlated with clinical parameters in 69 patients with systemic mastocytosis (SM). Based on cytomorphological features. four disti nct cell types were recorded: (i) typical tissue MC (round cells, well gran ulated, round central nuclei), (ii) atypical MC exhibiting elongated cytopl asmic extensions, oval nuclei with excentric position, and a hypogranulated cytoplasm with focal granule accumulation ('atypical MC type I'); (iii) at ypical MC with bi- or multilobed nuclei ('atypical MC type II'); and (iv) m etachromatically granulated blast-like cells. In the majority of cases with SM, the percentage of MC in bone marrow (bm) smears was less than 5% (of a ll nucleated bm cells), and the predominant types were typical MC or atypic al MC type I. In a smaller group of patients, the percentage of MC was grea ter than 5% and a significant subset of MC (greater than or equal to 10%) w ere classified as 'metachromatic blasts' and/or atypical MC type II. These patients had a significantly shorter survival (P < 0.05) and most of them w ere found to lack UP-like skin lesions. A percentage of MC greater than or equal to 20% was invariably associated with the diagnosis 'mast cell leukem ia'. Multivariate analysis confirmed the prognostic value of the cytology i n SM and identified the percentage of MC (of all nucleated bm cells) as an independent prognostic variable. These data suggest that cytomorphological assessment of bm MC in SM is an important diagnostic approach that may help to delineate between;variants of the disease. (C) 2001 Elsevier Science Lt d. All rights reserved.