Immunoperoxidase characterization of extramedullary plasmacytoma of the head and neck.

A retrospective analysis of 18 cases of extramedullary plasmacytoma (EMP) was done to characterize the type of immunoglobulin being synthesized by the neoplastic cells. The immunoperoxidase stain can be performed on previously fixed tissue and offers a means of predicting the likelihood of progression to multiple myeloma (MM). Tumors producing IgG make up the majority of cases of EMP in the literature and only 9% have progressed to MM. Smaller numbers of tumors producing other immunoglobulin classes have been studied, but it is clear that their prognosis is much more grave.