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The tumor is composed of diffuse sheets of immature plasma cells. Entrapped seminiferous tubules lined by only Sertoli cells were seen at the periphery of the tumor. The immunohistochemical profile was similar to that of multiple myeloma (strong expression of CD38, CD138, MUM1, and cytoplasmic light chains with kappa restriction; negative for CD19 and CD20). The differential diagnosis includes seminoma, spermatocytic tumor, and lymphomas with plasmacytic differentiation, including lymphoplasmacytic lymphoma, immunoblastic or plasmablastic large cell lymphoma, and marginal zone lymphoma of MALT type.