Extramedullary non-gastrointestinal plasmocytoma. An immunohistochemical study of sixteen cases.

Sixteen cases of extramedullary non-gastrointestinal plasmocytoma were studied for intracytoplasmic immunoglobulins by means of the immunoperoxidase-complex technique. Of the sixteen cases IgG class were observed in 4, IgM in one and IgA in 9 cases. Kappa light chains were found in 9 cases and lambda light chains in 6 cases. In one case a bitypic pattern of k- and lambda-positivity was encountered. In 2 cases only kappa light and no heavy chains were detected. The predominance of the IgA class in extramedullary, non-gastrointestinal plasmocytomas is in contrast to the prevalence of IgG type in multiple myeloma. The better possible behaviour of IgA-plasmocytomas is discussed further.