CD31 expression in plasmacytic/plasmablastic lesions.

Although CD31 has been considered one of the better, if not the best, immunohistochemical marker of endothelial cells and thereby vascular neoplasia, it is not unequivocally specific to this group of tumors. We examined CD31 staining in 34 plasmacytic lesions including 15 plasma cell myelomas, 1 extraosseous plasmacytoma, 10 plasmablastic variants of myeloma, 5 plasmablastic non-Hodgkin lymphomas, and 3 reactive plasmacytic infiltrates. All reactive plasma cellular infiltrates, 93% of plasma cell myelomas, 80% of plasmablastic variants of myelomas, and 20% of plasmablastic non-Hodgkin lymphoma cases were CD31 positive with usually diffuse and strong membranous staining. When ERG staining was performed, none were ERG positive. Plasmablastic variant of myeloma is another large cell malignancy that has the potential to be mistaken for a poorly differentiated epithelioid vascular neoplasm if CD31 is presumed to be an explicit marker of endothelial cells.