Primary cutaneous undifferentiated round cell tumor with concurrent polymyositis in a dog

Cutaneous poorly differentiated round cell tumor with concurrent, non suppurative, polymyositis was diagnosed in a Hovawart dog. Histochemical staining, immunohistochemistry and transmission electron microscopy findings suggest that tumors cells are of myeloid, or possibly Natural Killer cell, origin. The possibility that the concurrent polymyositis described may represent a pre-neoplastic or paraneoplastic process is discussed