Diagnostic and prognostic value of the MB2 monoclonal antibody in paraffin-embedded bone marrow sections of patients with multiple myeloma and monoclonal gammopathy of undetermined significance.

Routinely processed bone marrow biopsies of 59 patients with untreated multiple myeloma (MM) and of 41 patients with monoclonal gammopathies of undetermined significance (MGUS) were immunocytochemically studied with the MB2 monoclonal antibody. In 54 of 59 biopsies of patients with MM, most neoplastic plasma cells showed strong cytoplasmic positivity to MB2. In contrast, only three biopsies of patients with MGUS contained highly MB2-positive plasma cells, whereas the plasma cells in the remaining biopsies were either negative (18 of 41) or revealed a weak dot-like staining of the cytoplasm (20 of 41). Plasma cells in tonsillar tissue, gastric and duodenal mucosae, and bone marrow with reactive plasmacytosis were not stained with MB2. These findings suggest that MB2 helps to distinguish between MM and MGUS. Because the five MB2-negative patients with MM were all in stage III and had very short survival time, neoplastic plasma cell staining with MB2 could also have a prognostic significance.