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The immunohistochemical profile of testicular plasmacytoma is similar to that of multiple myeloma. It is a neoplasm of post-germinal center B-cell derivation with plasmacytic differentiation.
The tumor cells show strong expression of CD38, CD138 (syndecan-1), CD79a, VS38c, and MUM-1/IRF4. There is strong cytoplasmic expression of light chains with kappa or lambda restriction. Expression of CD56 is commonly seen. In typical cases, there is no expression of pan B-cell antigens such as CD19, CD20, PAX-5, nor CD45. Exceptions do occur. A small subset of myelomas expresses CD20.
The tumor cells show strong expression of CD38, CD138 (syndecan-1), CD79a, VS38c, and MUM-1/IRF4. There is strong cytoplasmic expression of light chains with kappa or lambda restriction. Expression of CD56 is commonly seen. In typical cases, there is no expression of pan B-cell antigens such as CD19, CD20, PAX-5, nor CD45. Exceptions do occur. A small subset of myelomas expresses CD20.