Histopathologic Characterization of Metastatic Ceruminous Gland Adenocarcinoma in a Dog

A 13-year-old spayed female American cocker spaniel dog was submitted to an animal hospital with a mass from left ear canal and enlarged left parotid lymph node. Given one-year history of odorous exudates and chronic otitis externa, total ear canal ablation was performed. Grossly, because of the neoplastic mass in both inner and outside of annular cartilage in external ear, vertical ear canal was severely narrowed. Histologically, there were numerous proliferated glands in the ear canal mass. Many neoplastic glands contained secretory vesicles on the free margin and necrotic cellular debris. Severe multifocal necrosis and strong invasion were also observed throughout the mass. Massive metastatic foci of glandular structures originated from ceruminous gland were presented in the enlarged parotid lymph node. Neoplastic glandular epithelia contained PAS-positive diastase-resistant eosinophilic cytoplasmic granules. Immunohistochemically, the neoplastic cells showed positive reactions for cytokeratin (CK) 7 and negative for CK 5/6. Based on the clinical implication and gross findings, histopathology and immunohistochemistry, this case was diagnosed as metastatic ceruminous gland adenocarcinoma in the American cocker spaniel.