Clinicopathologic study of cutaneous plasmacytoma.

Eight patients with skin tumor lesions composed of dense, predominantly plasma cell infiltrates were studied. Primary cutaneous plasmacytoma can be reactive (polyclonal) or neoplastic (monoclonal). In four of the patients skin lesions were associated with multiple myeloma. Specific skin lesions usually consisted of reddish or purple nodules located on the trunk. In one case the cutaneous lesions developed at the site of previous herpes zoster. Histologically, the cutaneous plasmacytic infiltrate was mainly diffuse and monomorphous. Most of the plasma cells were mature, but in some cases immature immunoblasts and mitoses were observed. Serum immunoelectrophoresis findings correlated with the monoclonality or polyclonality of the plasmacytoma. Presence or absence of systemic involvement cannot be predicted from the appearance of clinical lesions or from maturity of plasma cell infiltration in the skin.