Search

Objective: The previously reported kappa/lambda ratio cut-offs for plasma cell clonality by immunohistochemistry were in different values. This study aimed to identify the cut-offs with the highest accuracy for the diagnosis of multiple myeloma. Methods: Bone marrow specimens consecutively recruited between January 2011 and March 2019. The patients were at least 18 years old with clinical suspicion of multiple myeloma and had bone marrow plasma cell ≥10% by CD138 immunohistochemistry. The index test was immunohistochemical stains for plasma cell kappa/lambda ratio. The reference standard to classify as multiple myeloma required meeting any of the following (1) kappa/lambda ratio ≤1/16 or ≥16, (2) abnormal plasma cell morphology, and (3) monoclonal immunoglobulin . From 147 specimens (70 multiple myelomas and 77 reactive plasmacytosis), our cut-offs kappa/lambda ratio for light chain restriction at ≤1/7 or ≥9 yielded an area under the receiver operating characteristic curve of 1.0000 while ≤1/16 or ≥16 yielded 0.9643 ( Results: From 147 specimens (70 multiple myelomas and 77 reactive plasmacytosis), our cut-offs kappa/lambda ratio for light chain restriction at ≤1/7 or ≥9 yielded an area under the receiver operating characteristic curve of 1.0000 while ≤1/16 or ≥16 yielded 0.9643 ( p -value 0.0212). Conclusion: The cut-offs for kappa/lambda ratio at ≤1/7 or ≥9 for diagnosis of multiple myeloma yielded the highest diagnostic accuracy. The suggested cut-offs could be of potential value in resource-limited laboratories.

Background: Daratumumab (DARA) is a humanized Immunoglobulin G(IgG)1-kappa monoclonal antibody against CD38 antigen that is shown to improve outcomes in relapsed/refractory plasma cell myeloma (PCM) patients. Since CD38 is expressed by different hematopoietic elements, DARA has the potential to interfere with flow cytometric assessment of bone marrow specimens., Methods: Flow cytometric analysis of bone marrow samples from 10 PCM on DARA and 5 control samples was performed using two different antibody panels., Results: Bone marrow samples from PCM patients on DARA exhibited a population of CD19+ CD10+ B-lymphoid cells with kappa light chain restriction. Further morphological and immunophenotypic studies suggested that this population represents marrow hematogones. Marrow hematogones from control samples showed normal immunophenotypic profiles., Conclusion: DARA on the surface of hematogones interferes with flow cytometric clonality study leading to artifactual kappa light chain restriction, which can result in false interpretation of a concurrent clonal B-cell proliferation. In the era of rapidly growing list of therapeutic monoclonal antibodies, flow cytometry pathologists should be aware of potential interferences to avoid misdiagnosis. © 2019 International Clinical Cytometry Society., (© 2019 International Clinical Cytometry Society.)