IGM MYELOMA - CASE-REPORT WITH IMMUNOPHENOTYPIC PROFILE

Immunoglobulin (Ig)M myeloma is a distinct subtype of multiple myeloma (MM) displaying clinical and pathologic features of both MM and Walde nstrom's macroglobulinemia (WM) Although the immunophenotypic characte ristics of classic MM and WM have been reported, the surface antigen e xpression of IgM myeloma has not been reported. We report a case of Ig M myeloma end describe its Immunophenotypic profile using flow cytomet ry, The cells showed a hybrid MM-WM phenotype, strongly expressing CD3 8 but lacking CD45 and DR, typical for plasma cells; however, pan-B ce ll antigens CD20 and FMC7 as well as weak monoclonal surface Ig also w ere positive, resembling B-cell lymphoproliferative malignancies. Disc ordant B-cell antigen expression was present, in that pan-B antigens C D19 and CD22 were absent. In addition, B-cell activation antigen CD23, early B-precursor antigen CD10 and pan-T antigen CD5 were not express ed. Although CD20 and weak surface Ig expression have been reported in MM, FMC7 positivity has not been seen. The data therefore suggest tha t IgM myeloma may have a unique phenotype with characteristics of both MM and WM, (C) 1998 Wiley-Liss. Inc.