Identification of Immunoglobulin Light Chains in Canine Extramedullary Plasmacytomas by Thioflavine T and Immunohistochemistry

Abstract

Abstract. Extramedullary plasmacytomas were studied in 29 dogs. The site at which tumors occurred and the age and sex of the dogs were similar to those in previous reports. The skin of the digits, chin, ear, and lip represented the most common (17/29) tumor sites. Males and females were equally represented, and tumors occurred in middle-aged to old dogs (mean age, 9.0 years). A breed predilection was seen in the Cocker Spaniel (n = 7; 24%); Cocker Spaniels represented only 4% (210/4,725) of the submissions during the same period. Tumors were stained with immunohistochemical markers (λ light chain, K light chain) and thioflavine T. Immunoreactivity was limited to either λ or K light chains, consistent with a monoclonal plasma cell population. The majority of tumors expressed λ light chains, consistent with previously reported canine plasma cell dyscrasias. Thioflavine T cytoplasmic fluorescence was seen in the majority (18/29) of plasmacytomas and with inflammatory plasma cells present in control specimens. Other round cell neoplasms (lymphosarcoma, histiocytoma, and mastocytoma) were negative with thioflavine T, indicating that positive staining with thioflavine T was specific for plasma cells (neoplastic and inflammatory). This study confirms by immunohistochemistry that canine extramedullary plasmacytomas disproportionately express λ light chains and establishes thioflavine T staining as a rapid histochemical method for diagnosis of these tumors.The morphologic, clinical, and biological features of canine extramedullary plasmacytoma (EMP) have been reported 1,13,16,17,20,24 Most dogs were aged adults, and tumors developed most commonly on the mucocutaneous junction of the mouth, the skin between the digits, and on the external ear. 1,24 More than 90% of the dogs with cutaneous EMP were cured by surgical excision, indicating that these tumors were most likely benign. Multiple EMP were found in a small percentage of dogs but were not associated with progression to multiple myeloma. Only rarely did cases of canine EMP precede the development of multiple myeloma, 14,24 which is different from the clinical course seen in humans.In humans, long-term survival of 15 years without recurrence occurs in the majority of cases of EMP, 28 but in approximately 25% of the cases, EMP will develop into multiple myeloma. 18 When EMP precedes the development of multiple myeloma, an extended period (up to 10 years) may occur before clinical signs of bone involvement are noted. Secondary extramedullary involvement of the skin with primary multiple myeloma is rare. Immunohistochemical characterization of human EMP with immunoglobulin heavy and light chains reveals a monoclonal proliferation of plas-

Morphology and immunoreactivity of canine and feline extramedullary plasmacytomas

“…The previous studies revealed that American Cocker Spaniel, English Cocker Spaniel, Airdale Terrier, Kerry Blue Terrier, Scottish Terrier, Yorkshire Terrier, Golden Retriever, Labrador Retriever and mixed breeds are predisposed to EMP (Cangul et al 2002, Gupta et al 2014. The evaluated canine EMPs were seen more often in bitches than in males, in contrary to previous studies (Brunnert andAltman 1991, Cangul et al 2002).…”

Extramedullary plasmacytoma of the third eyelid gland in a dog

“…In dogs, the examination of plasmacytic infiltrates poses a problem for histopathological diagnosis, because the physiological λ : κ ratio in dogs already appears to indicate light‐chain restriction 17 . Some studies have demonstrated the monoclonal nature of the tumor 18,19 . The positivity to CD138 and λ light chain reveals B‐cell origin.…”

Immunohistochemical Detection of Multiple Myeloma 1/Interferon Regulatory Factor 4 (MUM1/IRF-4) in Canine Plasmacytoma: Comparison with CD79a and CD20

“…56,57 Immunohistochemical detection of immunoglobulin heavy and light chains has been the standard test for plasma cell differentiation. 1,4,5,13,29,35,38,42,45 However, nonspecific staining may result from adsorption of immunoglobulins to the cell surface, internalization by phagocytes, or binding of immunoglobulins to a variety of cell types via Fc receptors. 46 Although reactivity of CD79a in canine plasmacytoma and B-cell lymphomas is well established, there are large variations in the percentage of cases and number of cells stained with this marker, with up to 80% of plasmacytomas expressing CD79a.…”