Distribution of myeloma plasma cells in peripheral blood and bone marrow correlates with CD56 expression

There is a wide variation in the degree of marrow and blood involvement bet ween patients with multiple myeloma. Both of these parameters are known to be highly significant prognostic factors, and the differences between patie nts may be due to variable expression of adhesion molecules. To test this w e used three-colour now cytometry to study three adhesion molecules associa ted with myeloma, namely CD38, CD56 and CD138. The level of expression of t hese molecules was compared with the distribution of myeloma plasma cells i n bone marrow (n=59) and peripheral blood (n=26) in patients at presentatio n or relapse, The extent of marrow infiltration on the trephine biopsy corr elated inversely with CD56 expression (Mann-Whitney U Test, P=0.022); there was no difference in CD38 or in CD138 expression. CD56 expression also cor related inversely with the number of circulating plasma cells (linear regre ssion, R-2=0.4268. slope=-0.58, P=0.0003). Peripheral blood plasma cell num bers correlated weakly with bone marrow plasmacytosis, and inversely with C D38 expression, The level of CD56 expression by neoplastic plasma cells was assessed in 37 patients over a median of 11 months (range 6-25). There was no significant change in expression (Wilcoxon Signed Rank, P=0.6271). We c onclude that plasma cell CD56 expression is constant over the course of the disease; unlike CD138 expression, it is significantly linked to the degree of both bone marrow and peripheral blood involvement.