Frequent expression of haemopoietic and non-haemopoietic antigens by neoplastic plasma cells: an immunohistochemical study using formalin-fixed, paraffin-embedded tissue.

There is increasing evidence that neoplastic plasma cells express various haemopoietic and non-haemopoietic antigens. Since this issue could raise problems in diagnostic histopathology, we have investigated 51 cases of multiple myeloma (plasmacytoma) systematically with a broad panel of antibodies applicable on paraffin-embedded and mildly decalcified tissue. In approximately 90% of the cases the neoplastic plasma cells reacted with at least one antibody detecting haemopoietic antigens: MB2 (75%), DF-T1/CD 43 (59%), UCHL1/CD 45RO (47%), Ki-B3 (41%), anti-LCA/CD 45 (40%), L26/CD 20 (26%), 4KB5/CD 45RA (18%), Ber H2/CD 30 (10%), anti-neutrophil elastase (4%), anti-Leu-7/CD 57 (8%), Dako-M1/CD 15 (2%), KP1/CD 68 (2%) and anti-glycoprotein IIIa (2%). In approximately 70% of the cases the cells reacted with antibodies against non-haemopoietic antigens: anti-epithelial membrane antigen (65%), BMA120 (53%), anti-vimentin (44%), anti-pan-cytokeratin/KL1 (8%), anti-carcino-embryonic antigen (6%) and HMB45 (6%). Lack of awareness of the frequent expression of both haemopoietic and non-haemopoietic antigens by neoplastic plasma cells could lead to mis-diagnosis of plasmacytomas as malignant lymphomas or even as carcinomas or sarcomas.