An evaluation of immunohistologic stains for immunoglobulin light chains in bone marrow biopsies in benign and malignant plasma cell proliferations.

Bone marrow specimens from 226 patients with a variety of benign and malignant plasma cell proliferations were studied to assess the reliability of immunohistologic studies in their evaluation. The clonality of the bone marrow plasma cells was compared with results of serum and urine electrophoreses. Discordance was observed most frequently in cases in which a paraprotein was demonstrated, but no monoclonality was detected by immunoperoxidase (16 cases). Of these 16 cases, 9 had 5% or less bone marrow plasma cells. In only one case was the light chain class of the bone marrow plasma cells different from that of the paraprotein. If discordant cases with 5% or less plasma cells are eliminated, the overall concordance was 97%. The authors' findings indicate that immunohistologic studies for immunoglobulin light chains in Zenker-fixed decalcified bone marrow biopsy sections are reliable in the evaluation of patients with plasma cell proliferations when the marrow contains more than 5% plasma cells.