Characterization of Myeloma Cells by Means of Labeling Index, Bone Marrow Histology, and Serumβ2-Microglobulin

Abstract

The relationship between two cellular prognostic parameters of multiple myeloma, the plasma cell labeling index (LI%) and bone marrow histology was studied. The LI% as the percentage of monoclonal plasma cells in the S-phase was measured by bromodeoxyuridine incorporation using the anti-bromodeoxyuridine antibody BU-1. The histologic classification was based on six plasma cell types that allow prognostic grading as the Marschalko, small cell, cleaved, polymorphous, asynchronous, and blastic types. The biopsies also were used for estimating the degree of infiltration. Beta 2-microglobulin (IMx assay, Abbott, North Chicago, IL), the most significant serum parameter for myeloma also was measured for comparison. Bone marrow specimens and sera were obtained from 50 myeloma patients. Fourteen patients with smoldering myeloma were characterized by well-differentiated Marschalko or small cell type cells, a low LI% and a low beta 2-microglobulin concentration. Considering all myeloma patients, plasma cell type and degree of infiltration showed a significant correlation with LI% and beta 2-microglobulin concentration. Patients with plasma cells that were not mature cells of the Marschalko or small cell type revealed a high LI% or high beta 2-microglobulin level in 16 of 19 cases. However, a high LI% or high beta 2-microglobulin level could be detected in only 8 of 31 patients with plasma cells of the Marschalko or small cell type. Three of 21 stage I patients did not show the typical finding of a low LI%, low beta 2-microglobulin level, and a favorable grade. Stage II patients were not uniformly characterized by LI%, beta 2-microglobulin and plasma cell morphology. The percentage of nucleolated plasma cells was not associated with the LI%. Bone marrow histology, LI%, and beta 2-microglobulin concentration appear to be supplementary prognostic factors. If LI% and beta 2-microglobulin levels are not measured, a higher risk could be overlooked in cases with mature plasma cells.