An immunohistochemical study of canine extramedullary plasma cell tumours.

Twenty-three cases of dog plasma cell tumours were investigated for the presence of monoclonal cytoplasmic immunoglobulin light chain types and heavy chain classes. The peroxidase-antiperoxidase method was applied to formalin-fixed, paraffin-embedded tissues, available as stored blocks. Twenty tumours showed a monoclonal light chain type and heavy chain class pattern, two showed a monoclonal light chain type and a biclonal heavy chain class pattern, findings which confirmed the neoplastic nature of the plasma cells. One tumour did not stain with any of the antisera. The results indicate that the method reliably establishes the monoclonality and, consequently, the neoplastic nature of plasma cell proliferations.