Detection of clonality with κ and λ immunohistochemical analysis in cutaneous plasmacytomas

• Context. - Cutaneous plasmacytomas rarely occur in the setting of multiple myeloma. However, since poorly differentiated lesions may resemble other neoplasms, such as carcinoma, melanoma, and lymphoma, the diagnosis of cutaneous plasmacytoma may be difficult. Objective. - To demonstrate clonality using κ and λ immunohistochemical analysis in cutaneous plasmacytomas and to ascertain whether or not interpretation is hindered by background staining. Design. - Pathology reports of all patients with the diagnosis of multiple myeloma were reviewed. Twelve patients had cutaneous lesions diagnosed as plasmacytoma, and these lesions were analyzed for light chain restriction with κ and λ immunohistochemical analysis. Results. - In most cases (11 of 12), monoclonality was demonstrated. In the remaining case, monoclonality could not be established because most cells did not stain for either κ or λ. Conclusions. - Light chain restriction can be demonstrated in most multiple myeloma-related cutaneous plasma-cytomas, establishing the neoplastic nature of the infiltrate.