Immunophenotyping of cutaneous extramedullary plasmacytoma in two dogs

Abstract

Skin biopsied tissues from two dogs, initially diagnosed as hemophagocytic histiocytic sarcoma (HHS) by histopathology, were immunostained with a series of antibodies against lambda light chains, kappa light chains, multiple myeloma oncoprotein 1 (MUM-1), CD-3, paired box 5 (PAX-5), E-cadherin and lysozyme. Heteroduplex polymerase chain reaction for antigen receptor rearrangements (hPARR) was additionally performed on formalin-fixed paraffin-embedded (FFPE) tissues to rule out lymphomas from histiocytomas. Results showed that both cases were immunopositive for lambda light chains, MUM-1, PAK-5 and lysozyme, indicating a diagnosis of extramedullary plasmacytoma (EMP). Moreover, negative PCR result provided additional evidence confirming the diagnosis. Even though hPARR could not differentiate between histiocytomas and EMP, it could rule out these tumors as malignant lymphomas. This report emphasizes the advantage of using a panel of antibodies, besides histopathology, for HHS diagnosis.