A retrospective study of canine oral extramedullary plasmacytoma over a 15-year period (July 2004 - July 2019): treatment, histologic parameters, and clinical outcomes.

A total of 45 cases of canine oral extramedullary plasmacytomas (EMPs) presented to a tertiary referral institution over a 15-year period were examined. Histologic sections of 33 of these cases were examined for histopathologic prognostic indicators. Patients underwent variable treatment including surgical intervention, chemotherapy, and/or radiation therapy. Long term survival was observed in the majority of dogs with a median survival time of 973 days (2-4315 days). However, almost 1/3 of dogs had progression of plasma cell disease, including 2 cases with myeloma-like progression. Histologic characterization of these tumors did not reveal criteria to predict tumor malignancy. However, cases without tumor progression did not exceed 28 mitotic figures in ten 400x fields (2.37mm 2 ). All cases with tumor related death showed at least moderate nuclear atypia. Oral EMPs may represent a local manifestation of systemic plasma cell disease or singular focal neoplasia.