Mature plasma cells as indicator of better prognosis in multiple myeloma. New methodology for the assessment of plasma cell morphology

The relationship between plasmablastic cells and outcome in multiple myelom a (MM) has been established for nearly 15 years. Bur the assessment of thes e cells is not easy to perform and it allows the identification of only a s mall proportion of patients. We investigated the plasma cell morphology usi ng a progressive evaluation of consecutive criteria: nucleolus, chromatin a nd nuclear-cellular ratio (N/C). The combination of these three items produ ces a subclassification where four cellular subtypes identify 93% of the pl asma cells, and these subtypes are related to the outcome. The interest of this methodology is to be based on the mature plasma cells that are easier to identify than the plasmablastic cells. These new cell subtypes introduce a new classification for patients: Group 1 includes patients with at leas than 66% mature plasma cells (P000). Both Group 2 and 3 have less than 66% P000 and are separated by their degree of maturation (Proplasma I greater t han or equal to Proplasma II + plasmablastic). The distinction of these thr ee groups of patients is highly related to the prognosis (P < 10(-4)). Thes e results have been confirmed on a second group of patients coming from a d ifferent institution. In conclusion, we propose a new methodology for the p lasma cell evaluation in MM, that is based on the morphological criteria an d that has the advantage of identifying an intermediate (30%) subgroup of p atients with a prognostic significance. (C) 1999 Elsevier Science Ltd. All rights reserved.