OLIGOCLONAL PROTEIN BANDS AND IG ISOTYPE SWITCHING IN MULTIPLE-MYELOMA TREATED WITH HIGH-DOSE THERAPY AND HEMATOPOIETIC-CELL TRANSPLANTATION

Multiple myeloma (MM) is usually characterized by production of a sing le serum monoclonal protein of constant isotype and light-chain restri ction. Multiple Ig isotypes and isotype switches, which are rare in un treated patients, are reported to be more common in patients undergoin g myeloablative therapy. These additional protein bands, detected by i mmunofixation electrophoresis (IFE), could be due to altered paraprote in production by the malignant plasma cell clone or oligoclonal lg pro duction during recovery of B-cell function after myeloablative therapy . We analyzed abnormal protein bands (APB), distinct from the presenti ng paraprotein, in 550 patients receiving high-dose therapy with autol ogous hematopoietic cell transplantation at a single institution. Fift y-five patients (10%) had APB, 48 had oligoclonal bands (OB), and 23 h ad an apparent isotype switch (IS) on IFE (16 had both OB and IS). Mor phologic and flow cytometric examination of bone marrow in 17 patients with IS showed no evidence of a clonal plasma cell isotype switch. Pa tients with APB had significantly higher complete response to therapy (67% v 37%, P = .001). To assess the independent prognostic relevance of APB, a multivariate analysis was performed among 471 patients survi ving at least 12 months from first transplant (all patients developing APB had done so by 12 months from first transplant). APB (in 50 patie nts) was a favorable feature for both event-free (rank 3, P = .004) an d overall survival (rank 3, P = .0005). We propose that OB and IS are likely to he due to recovery of Ig production rather than alterations in the biology of the malignant plasma cell clone. (C) 1998 by The Ame rican Society of Hematology.