Flow cytometric differentiation of abnormal and normal plasma cells in the bone marrow in patients with multiple myeloma and its precursor diseases.

Flow cytometric (FC) enumeration of abnormal plasma cells (APCs) for diagnosis and prognostication of plasma cell dyscrasias (PCD) is challenging. We studied antigen expression in normal plasma cells (NPC) (N = 34) and APC in a series of unselected PCD (N = 59). NPC subpopulations often demonstrated CD19(-), CD20(+), CD45(-) or dim and CD56(+), an immunophenotype observed in PCD. However abnormal CD81 was only observed in APCs (APC detection sensitivity 95%; specificity 100%). We evaluated differences in antigen expression patterns among MGUS (N = 14), SMM (N = 35) and MM (N = 10), finding the combination of CD45 and CD56 helpful in differentiating MGUS from SMM and MM (p = 0.0002).