Characteristics of unexpected protein bands in multiple myeloma patients after autologous stem cell transplantation

Abstract Objectives The aim of this study is to investigate the characteristics of unexpected protein bands (UPBs) in patients with multiple myeloma (MM). Design and methods Individuals diagnosed with MM ( n  = 193) were enrolled. Their medical records and IFE patterns were reviewed. Results Of the patients that underwent ASCT, 54% developed UPBs. The median time for UPB appearance and duration was 1.8 and 5.7 months, respectively. IFE revealed 74.1% of UPBs to be of the immunoglobulin G type and 72.2% to be of the κ-type. At UPB appearance, 42.6% of patients were defined as sCR or CR, and 50.0% of the patients satisfying the CR criteria had an abnormal FLC ratio. Of the patients who developed UPBs, five relapsed. Among these, four patients showed disappearance of the previous IFE oligoclonality and reappearance of the original paraprotein at relapse. Conclusions Close follow-up of UPBs is critical for evaluating MM therapeutic response and disease progression. The presence of monoclonal bands may indicate relapse of disease, but in the vast majority of cases with UPBs, it does not; instead, it most likely represents a transient phenomenon caused by the immune response.