Apocrine Sweat Gland Ductal Adenoma with Sebaceous Differentiation in a Dog

A 7-year-old male, Border Collie, developed a firm mass, measuring approximately 1？cm in diameter, in the left buccal skin. Histologically, the mass was composed of ductal structures lined by bilayered luminal epithelial and basaloid tumor cells along with a few nests of sebaceous cells. Immunohistochemical staining revealed that the luminal epithelial tumor cells were positive for cytokeratin (CK, CAM5.2) and CK19 but not for CK14 or p63. In contrast, the basaloid tumor cells were positive for CK14, p63, and αSMA but not for CK19 or CAM5.2. CK8 expression was observed in both luminal epithelial and basaloid tumor cells. The tumor cells with sebaceous differentiation were positive for CK14 but not for the other markers. This is the first case of an apocrine sweat gland ductal adenoma with sebaceous differentiation occurring in the buccal skin of a dog. 1. Introduction Apocrine sweat gland tumors are rather common in dogs and tend to occur on the head, neck, and limb. Approximately 70% of canine apocrine sweat gland tumors are benign in nature [1]. Benign tumors of the apocrine sweat gland are classified as apocrine adenomas, complex and mixed apocrine adenomas, or apocrine ductal adenomas [2]. Apocrine ductal adenomas in dogs are uncommon benign neoplasms and accounted for only 0.3% of canine skin tumors in a large survey [1]. In dogs, sebaceous differentiation has been described in five cases of mammary gland tumors [3–6]. However, to the authors’ knowledge, a nonmammary-associated apocrine tumor with sebaceous differentiation in dog has not been previously reported. 2. Case Report A 7-year-old male, Border Collie, developed a firm mass in the left buccal skin, which was surgically removed and submitted to the Department of Veterinary Pathology, Nippon Veterinary and Life Science University (Tokyo, Japan), for histopathological examination. Grossly, the mass was approximately 1 cm in diameter, and a cut surface of the mass appeared homogeneously greyish-white in color. A physical examination including complete blood count and a routine serum biochemical profile revealed no further abnormalities. Detailed radiographic and X-ray examinations did not reveal any mass suggestive of a tumor in the thoracic and abdominal cavities. No tumor recurrence or metastasis was noted after 9 months of surgical excision. Additional therapy was not performed. The excised mass was fixed in 10% neutral buffered formalin, embedded in paraffin wax, cut into 4？μm sections, and stained with hematoxylin and eosin (HE), periodic acid-Schiff (PAS), alcian blue, and oil red O