The neoplastic cells have indistinct borders with moderate amounts of eosinophilic to lightly basophilic cytoplasm. There is often moderate anisokaryosis with frequent multinucleation. The mitotic rate is variable. Cells recognizable as typical plasma cells, frequently with prominent Russell bodies, often can be found near the periphery. Deposits of amyloid are occasionally found within the neoplasm.
Plasmacytomas are generally benign.
If incompletely excised, they may recur locally. Rare instances of metastasis have been reported. Prognostic value of histopathological grading in canine extramedullary plasmacytomas. The skin and appendages. A mass was excised from the tailhead area, recurred, and was excised again 4 months later.