The incidence of phagocytizing plasma cells in malignant plasma cell dyscrasias

Bone marrow smears from 401 patients with malignant plasma cell disorders (MPCD) were examined to evaluate the incidence of phagocytosis by plasma cells and to elucidate the pathogenesis of this phenomenon. Phagocytizing plasma cells were observed in 6 patients (1.6%), 1 of whom had plasma cell leukaemia, from a pool of 382 patients with multiple myeloma that included 7 with plasma cell leukaemia, but not in those with other types of MPCD. In 1 of the 6 cases, the plasma cells acquired phagocytizing ability in the terminal stage of the illness. The incidence of phagocytizing plasma cells in multiple myeloma was higher than might have been expected, judging from a small number of previous reports concerning phagocytosis by plasma cells. The incidence of phagocytizing plasma cells in plasma cell leukaemia (1:7) was not statistically greater than that in non-leukaemic multiple myeloma (5:375).