Immunohistological diagnosis of plasma cell myeloma based on cytoplasmic kappa/lambda ratio of CD138-positive plasma cells.

For differentiating reactive plasmacytosis from clonal plasma cell neoplasms such as plasma cell myeloma (PCM), it is important to determine the expression of the cytoplasmic light chain accurately. Through retrospective analysis, we studied the cytoplasmic kappa/lambda ratio of CD138-positive plasma cells in bone marrow from 50 patients with PCM and 50 controls by immunohistological analysis. The percentage of cytoplasmic light chain immunoreactive cells out of the total plasma cell population was shown by a novel quantitative image analysis approach using an Aperio ScanScope CS and the Membrane v9 algorithm. PCM cells were distinguished from normal plasma cells by cut-off levels between 0.35 and 5.5, a sensitivity of 100% and a specificity of 98.0%. Detection of the cytoplasmic kappa/lambda ratio of CD138-positive plasma cells could be a useful tool for simple, efficient and accurate diagnosis of PCM.