BRIEF REPORT

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

Correspondence to: Hinke A.B. Multhaupt, Dept. of Pathology, Pennsylvania Hospital, 800 Spruce Street, Philadelphia, PA 19107. E–mail: himult@pahosp.com

	Summary

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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 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 CD79. 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. (J Histochem Cytochem 49:791–792, 2001)

Key Words: plasmacytoma, mitosis, immunophenotyping, flow cytometry

	Introduction

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We present a case of a plasmacytoma with an atypical immunophenotype and histologic features. The biopsy material for this report came from a patient with sudden onset of pain from a lytic lesion in the left proximal humerus. Flow cytometric and paraffin immunoperoxidase studies were performed on the tissue.Hematoxylin and eosin-stained sections showed a lymphoproliferative lesion composed of large lymphoid cells, some exhibiting plasmacytoid and immunoblastic features (Fig 1a). There were many mitoses. Immunohistochemical staining was positive for CD45 (LCA; Fig 1b), CD43 (MT1; Fig 1c), CD56 (N-CAM; Fig 1g), and cytokeratin CAM5.2 (Fig 1h). There was also clonal staining for light chains (Fig 1f). In addition, flow cytometry showed positivity for CD13, CD33, CD38, and CD138. Significant negative markers include CD20 (L26), CD45RO (UCHL-1; Fig 1d), and CD79 (Fig 1e).

View larger version (154K): [in this window] [in a new window]   Figure 1. Photomicrograph of the plasmocytoma presented, stained with (a) hematoxylin and eosin and by immunohistochemistry for (b) CD45 (LCA), (c) CD43 (MT1), (d) CD45RO (UCHL-1), (e) CD79, (f) light chains, (g) CD56 (N-CAM), and (h) cytokeratin CAM5.2. Hematoxylin counterstain. Original magnification x100.

Neoplastic plasma cells, like normal plasma cells, usually lack the surface B-cell antigen. The absence of staining for leukocyte common antigen (LCA) and B-cell surface antigens CD19 and CD20 is highly characteristic (Strickler et al. 1988 ; Wotherspoon et al. 1989 ). Conversely, the B-cell antigen CD79, normally expressed in plasma cells, is demonstrable in a significant proportion of cases. Staining with CD38 is variable. CD56 (N-CAM) is a natural killer cell-associated antigen commonly expressed in multiple myeloma and typically absent in monoclonal gammopathy of undetermined significance, thus being a reliable discriminator between myeloma and MGUS (Van Camp et al. 1990 ). Moreover, low CD56 expression predicts high levels of marrow and blood tumor involvement, both poor prognostic factors (Davies et al. 1997 ).

Staining with T-cell markers is unusual but reports of plasmacytomas staining with CD43 and CD45RO do exist (Petruch et al. 1992 ). In a study using a standard antibody screening panel that includes L26 (CD20), Leu22 (CD43), and UCHL-1 (CD45RO), 17 cases with a "CD43 only" phenotype were identified, with two of these cases being plasmacytomas (Segal et al. 1992 ). Cytokeratin immunoreactivity in plasmacytomas is generally considered to be rare (Sewell et al. 1986 ). However, in a study looking at 14 plasma cell tumors, including solitary plasmacytomas and multiple myelomas, five of the cases showed reactivity for cytokeratin, thus confirming that anti-cytokeratin reactivity by plasma cell tumors is more common than was originally believed and may represent an important diagnostic pitfall (Wotherspoon et al. 1989 ).

Myeloma may occasionally present with aberrant expression of myelomonocytic antigens such as CD11b, CD13, CD14, CD15, and CD33 (Grogan et al. 1989 ; Epstein et al. 1990 ). These antigens are preferentially expressed in two types of neoplasms, i.e., indifferentiated ALL and mature B-cell lymphoproliferative disorders (Nakase et al. 1996 ). The expression of these antigens may be related to a poor prognosis (Ruiz-Arguelles and San Miguel 1994 ).

The unusual features of the plasmacytoma we present illustrate potential diagnostic pitfalls. Although plasmacytomas with aberrant expression of myeloid markers, T-cell markers, and cytokeratin have been described, our case may represent a plasmacytoma with a unique immunophenotype. The significance of such an unusual lesion is not fully understood, and further classification of this lesion and other similar lesions may be useful in determination of patient prognosis and management.

	Footnotes

Presented in part at the Joint Meeting of the Histochemical Society and the International Society for Analytical and Molecular Morphology, Santa Fe, NM, February 2–7, 2001.

Received for publication December 8, 2000; accepted February 16, 2001.

	Literature Cited

Top Summary Introduction Literature Cited

Davies FE, Jack AS, Morgan GJ (1997) The use of biological variables to predict outcome in multiple myeloma. Br J Hematol 99:719-725[Medline]

Epstein J, Xiao H, He X-Y (1990) Markers of multiple hematopoietic cell lineages in multiple myeloma. N Engl J Med 322:664-668[Abstract]

Grogan TM, Durie BGM, Spier CM, Richter L, Vela E (1989) Myelomonocytic antigen positive multiple myeloma. Blood 73:763-769[Abstract/Free Full Text]

Nakase K, Kita K, Shiku H, Tanaka I, Nasu K, Dohy H, Kyo T, Tsutani H, Kamada N (1996) Myeloid antigen, CD13, CD14, and/or CD33 expression is restricted to certain lymphoid neoplasms. Am J Clin Pathol 105:761-768[Medline]

Petruch UR, Horny HP, Kaiserling E (1992) Frequent expression of haemopoietic and non-haemopoietic antigens by neoplastic plasma cells: an immunohistochemical study using formalin-fixed, paraffin-embedded tissue. Histopathology 20:35-40[Medline]

Ruiz–Arguelles GJ, San Miguel JF (1994) Cell surface markers in multiple myeloma. Mayo Clin Proc 69:684-690[Medline]

Segal GH, Stoler MH, Tubbs RR (1992) The "CD43 only" phenotype. An aberrant, nonspecific immunophenotype requiring comprehensive analysis for lineage resolution. Am J Clin Pathol 97:861-865[Medline]

Sewell HF, Thompson WD, King DJ (1986) IgD myeloma/immunoblastic lymphoma cells expressing cytokeratin. Br J Cancer 53:695-696[Medline]

Strickler JG, Audeh MW, Copenhaver CM, Warnke RA (1988) Immunophenotypic differences between plasmacytoma/multiple myeloma and immunoblastic lymphoma. Cancer 61:1782-1786[Medline]

Van Camp B, Durie BG, Spier C, De Waele M, Van Riet I, Vela E, Frutiger Y, Richter L, Grogan TM (1990) Plasma cells in multiple myeloma express a natural killer cell-associated antigen: CD56 (NKH-1;Leu-19). Blood 76:377-382[Abstract/Free Full Text]

Wotherspoon AC, Norton AJ, Isaacson PG (1989) Immunoreactive cytokeratins in plasmacytomas. Histopathology 14:141-150[Medline]

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