In domesticated species, extramedullary plasmacytomas are most commonly diagnosed in dogs; however, they have also been reported in cats, ferrets, horses, sheep, and Syrian hamsters.4 In dogs, extramedullary plasmacytomas typically involve the skin or oral cavity, but GI, tracheal, and brain plasmacytomas have also been reported.1
In dogs, extramedullary plasmacytomas are rarely associated with systemic disease. In only ≈1% of canine cases do the neoplastic plasma cells of a plasmacytoma secrete immunoglobulins, which often causes hyperglobulinemia.1,5 Generally, plasmacytomas are benign and rarely recur when surgically excised.1 There is no proven progression or connection between extramedullary plasmacytomas and myelomas in dogs.5 A series of case reports on colorectal plasmacytomas demonstrated that these neoplasms clinically behave similarly to extramedullary plasmacytomas in other locations.6
The treatment of choice in plasmacytoma cases is complete surgical excision, which is also generally the sole treatment, as recurrence is rare. For cases in which complete excision is not possible or in cases of regrowth, a full course of radiation or chemotherapy has been reported to improve survival times.7 The recommended chemotherapy treatment includes melphalan, cyclophosphamide, and steroids.7