Fig. 5. A. A histopathologic exam demonstrates diffuse proliferation of atypical plasmacytoid cells (H&E stain). Immunohistochemical staining revealed that the tumor cells were negative for CD20 (B), but positive for CD138 (C), a plasma cell marker. D. Of the two types of immunoglobulin light chain, only the kappa chain showed immunoreactivity to tumor plasma cells (A–D, original magnification 400×).
