Primary cutaneous plasmacytoma: a role for a triggering stimulus?

Summary Primary cutaneous plasmacytoma is a rare type of cutaneous B‐cell lymphoma, characterized by clonal proliferation of plasma cells, that primarily develops in the skin. Five cases have been described to date in which a local triggering stimulus may be involved in development of this skin tumour. We describe the case of a primary cutaneous plasmacytoma localized to the lower lip. This site had been affected for 15 years with recurrent herpes simplex virus‐1 infection. Neoplastic plasma cells were found to be bcl‐2‐positive. We hypothesize that chronic stimulation of keratinocytes by herpes simplex virus‐1, possibly through toll‐like receptors, may have favoured the release of cytokines (e.g. interleukin‐6) able to induce plasma cell proliferation, transformation and survival.