A NEW PHENOTYPIC CLASSIFICATION OF BONE-MARROW PLASMACYTOSIS

Here, we propose a new phenotypic classification of bone marrow plasma cytosis. By 2-color phenotypic analysis with FITC anti-CD38 and PE ant i-CD19, -CD56, -VLA-5 or MPG-1 antibody, plasma cells are easily ident ified on the histogram, even though no more than 1% of plasma cells ar e found in the bone marrow. Hence, plasma cells are phenotypically cla ssified into polyclonal (reactive) (CD19(+)CD56(-)) or monoclonal (neo plastic) plasma cells (mostly CD19(-)CD56(+)), and furthermore immatur e (VLA-5(-)MPC-1(-)), intermediate (VLA-5(-)MPC-1(+)) and mature plasm a cells (VLA-5(+)MPC-1(+)). According to these findings, plasmacytosis in the bone marrow can be classified into polyclonal marrow plasmacyt osis (POMP) and monoclonal marrow plasmacytosis (MOMP) states. The MOM P state is further subclassified into MOMP-1 and MOMP-2, MOMP-3 and MO MP-4; MOMP-1 is defined by co-existence of monoclonal plasma cells and polyclonal plasma cells, and MOMP-2 to MOMP-4 are dependent on increa sed proportions of VLA-5(-)MPC-1(-) immature myeloma (plasma) cells. W e found that the cases of benign monoclonal gammopathy (BMG) according to the conventional classification were in the MOMP-1 state, and myel omas could be classified into the MOMP-2 to MOMP-4 state. Subclassific ation of the MOMP state may be useful in determining the prognosis of myelomas, where an increase in immature myeloma cells is reported to c orrelate well with their aggravation during the clinical courses. Ther efore, this new phenotypic classification of bone marrow plasmacytosis (POMP and MOMP-1 to MOMP-4) will contribute to differential diagnosis and understanding of therapeutic responses and prognosis in myelomas.