Background: Cutaneous plasmacytosis and systemic plasmacytosis are rare entities arising primarily in patients of Japanese descent. The origin and exact pathogenesis are poorly understood. Objective: We sought to determine clinicopathologic features of cutaneous and systemic plasmacytosis. Methods: We describe the clinicopathologic features of 6 patients with cutaneous plasmacytosis with or without systemic involvement (male:female = 3:1; mean age: 49.7 years; median age: 50.5 years; age range: 29-64 years). Results: Patients presented clinically with multiple, red-brown infiltrated plaques and flat tumors, mainly located on the trunk. Histology revealed in all cases the presence of clusters of mature plasma cells within the dermis. Lymphoid follicles with reactive germinal centers were seen in 3 cases. Five cases showed the expected polyclonal expression of immunoglobulin light chain by the plasma cells, but monoclonality was observed in 1 case, thus showing overlapping features with cutaneous marginal zone lymphoma. One patient revealed overlapping features with multicentric Castleman disease. Limitations: This was a retrospective study on a relatively small number of patients. Conclusions: Despite typical clinical presentation, some of our patients presented with histopathologic and immunohistochemical features that deviated from the conventional appearance. Our observation confirms and expands previous observations of this elusive entity, suggesting that the spectrum of clinicopathologic presentations may be wider than previously recognized.
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