Flow cytometric detection of neoplastic plasma cells.

(A) The gating strategy used to detect plasma cells, designed to exclude the majority of contaminating events (particularly B-progenitor cells, apoptotic cells, and cellular debris) common in posttreatment samples, described in detail in “Patients and methods.” (B) Representative plots from patients at 3 months after transplantation. The top row shows a patient whose bone marrow sample contains only normal phenotype (CD19⁺CD56^dim) plasma cells. The middle row shows a sample with only neoplastic phenotype (CD19⁻ or CD19⁺CD56⁺) plasma cells. The bottom row shows a sample containing mostly normal plasma cells with a detectable neoplastic population that represents 15% of total plasma cells.