Morphologic heterogeneity and plasmablastic transformation in advanced plasmacytic/plasmablastic myeloma: a study of 35 serial bone marrow biopsies in 9 patients.

Thirty-five bone marrow biopsies were performed in 9 patients with plasmacytic/plasmablastic myeloma stage IIIA of the Durie and Salmon classification. The cytologic and/or histologic transformation observed in the serial bone marrow biopsy specimens of 3 patients reflected an aggravation of the disease, and was expressed as an increase of bone marrow plasmablasts associated with a gradual decrease or even disappearance of the plasmacytic component. Beyond 50% of bone marrow plasmablasts, the plasmablastic myeloma represented a more aggressive phase in the course of the disease. In 2 patients this transformation was manifested by the development of extramedullary lesions. The possibility of chemotherapy influencing the progression of the plasmablastic clone by destroying the initial plasmacytic clone cannot be ruled out. These results are not devoid of therapeutic implications. They also emphasize the need for serial bone marrow biopsies for better detection of transformation into a less favorable cytologic and/or histologic type of myeloma.