LAUSR

Serum monoclonal immunoglobulin (M‐Ig) is a hallmark of multiple myeloma (MM) and is used as a biomarker of treatment response. Until now, we have learned that deep response characterized by a disappearance of M‐Ig, defined as complete response (CR), is associated with a long‐term survival in patients with MM. On the other hand, we also know that there are patients who relapse early after obtaining a CR, and there are others who remained stable without obtaining a CR. Such intriguing phenomena may likely be provoked by an immune status of the bone marrow milieu surrounding a tumor clone. Serum heavy/light chain (HLC) assay, which can quantify a minute amount of different HLC pairs of three immunoglobulin isotypes including IgG kappa, IgG lambda, IgA kappa, IgA lambda, IgM kappa, and IgM lambda, separately, is a breakthrough new method to assess not only M‐Ig but also uninvolved normal Ig in serum. In the present study, we assessed response to treatment according to the IMWG response criteria in patients with MM using the conventional methods comprising immunofixation electrophoresis (IFE) and free light chain (FLC) assay and compared with the results of the HLC assay. This is a cooperative, retrospective study and included patients with newly diagnosed symptomatic MM with IgG or IgA isotypes who had blood samples stored during the disease course from the time of diagnosis and until achievement of best response for the comparison of the results obtained by IFE, FLC, and HLC measurements. The study patient cohort consisted of 71 patients diagnosed and treated between June 01, 2016, and June 30, 2017, at any one of the hospitals belonging to the Japanese Society of Myeloma. This study was conducted in accordance with the ethical guidelines of the Declaration of Helsinki and was approved by the institutional Review Board of hospitals. HLC concentrations and ratios were considered abnormal if they were outside of the reference ranges determined by the manufacturer (The Binding Site, Birmingham, UK). Abnormal HLC ratio (rHLC) of a given intact immunoglobulin was identified as indicating the presence of clonality of that immunoglobulin. Written informed consent was obtained from each patient before study enrollment. We evaluated rHLC in each of the 71 patients with respective response status according to the IMWG response criteria evaluated at the time of their best response. The result is shown in Figure 1. Out of the 21 patients in whom CR or better was achieved, 17