Plasmacytoma with Aberrant Expression of Myeloid Markers, T-cell Markers, and Cytokeratin

• Published in: The journal of histochemistry and cytochemistry Vol. 49; no. 6; pp. 791 - 792
• Main Authors: Shin, Jung S, Stopyra, Gary A, Warhol, Michael J, Multhaupt, Hinke A.B
• Format: Journal Article
• Language: English
• Published: Los Angeles, CA Histochemical Soc 01-06-2001; SAGE Publications
• Subjects: Antigens, Differentiation, T-Lymphocyte - isolation & purification; Antigens, Neoplasm - isolation & purification; Bone Neoplasms - diagnosis; Humans; Humerus - pathology; Immunophenotyping; Keratins - isolation & purification; Plasmacytoma - diagnosis; flow cytometry; mitosis; immunophenotyping; plasmacytoma
• ISSN: 0022-1554; 1551-5044
• DOI: 10.1177/002215540104900613

Plasmacytomas are localized neoplastic proliferations of monoclonal plasma cells. When multifocal, the process is referred to as multiple myeloma. These lesions exhibit a pattern of antigen expression and cytomorphology that usually leads to a ready diagnosis. However, potentially troublesome variations in immunophenotype occur. We describe a case of a plasmacytoma from a patient who presented with sudden onset of pain and a lytic lesion of the left proximal humerus. Hematoxylin and eosin-stained sections showed a lymphoproliferative lesion composed of large lymphoid cells, some with plasmacytoid and immunoblastic features. The lesion also showed significant mitotic activity. Immunohistochemical staining was positive for CD45 (LCA), CD56 (N-CAM), CD43 (MT1), and cytokeratin CAM5.2. There was also clonal staining for λ light chains. In addition, flow cytometric analysis showed positivity for myeloid markers such as CD13, CD33, CD38, and CD138. Significant negative markers include CD20 (L26), CD45RO (UCHL-1), and CD79α. The unusual phenotypic features of this plasmacytoma illustrate potential diagnostic pitfalls. It is important to fully study such lesions to correctly classify them, because this has significant impact on prognosis and management.