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
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 [
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
Histologically, the mass was well demarcated and encapsulated. It consisted of various nodules and proliferating nests mainly composed of bilayered ductal structures with an inner layer of cuboidal to columnar luminal epithelial tumor cells and an outer layer of basaloid tumor cells separated by a thin fibrous stroma (Figure
Histopathological appearance of the buccal mass. The mass is composed of the ductal structures lined by the bilayered luminal epithelial and basaloid tumor cells. Hematoxylin and eosin (HE). Bar = 100
Sebaceous differentiation observed within the apocrine ductal adenoma. Sebaceous cells are characterized by abundant, clear, and vacuolated cytoplasm and a centrally located nucleus surrounded by basaloid cells in the apocrine ductal adenoma. HE. Bar = 50
As shown in Table
Summary of immunohistochemical findings.
Tumor cell type | CAM5.2 | CK8 | CK14 | CK19 | p63 |
|
---|---|---|---|---|---|---|
Luminal cells | + | + | − | + | − | − |
Basaloid cells | − | + | + | − | + | + |
Sebaceous-like cells | − | − | + | − | − | − |
Luminal tumor cells are positive for CK19. Immunohistochemistry for CK19 with hematoxylin counterstain. Bar = 50
Basaloid tumor cells and cells showing sebaceous differentiation are positive for CK14. Immunohistochemistry for CK14 with hematoxylin counterstain. Bar = 50
Basaloid tumor cells are positive for p63. Immunohistochemistry for p63 with hematoxylin counterstain. Bar = 50
Both luminal and basaloid tumor cells are positive for CK8. Immunohistochemistry for CK8 with hematoxylin counterstain. Bar = 50
On the basis of the histological and immunohistochemical findings, the tumor was diagnosed as an apocrine sweat gland ductal adenoma with sebaceous differentiation. According to the World Health Organization classification of epithelial and melanocytic tumors of the skin of domestic animals, benign tumors of the apocrine sweat gland are classified as apocrine adenomas, complex and mixed apocrine adenomas, or apocrine ductal adenomas [
CK19 and CAM5.2 are useful markers of luminal cell markers, while CK14, p63, and
This tumor appeared
The origin of the sebaceous component in this tumor was unclear. However, previous studies suggested that tumor basaloid cells can differentiate into sebaceous epithelial cells and that cutaneous stem cells might give rise to sebocytes in canine mammary tumors [
The authors declare that there is no conflict of interests.
The authors would like to thank Dr. Hidemi Kitagawa for providing the follow-up information and the tumor specimen for this study and Drs. Yoko Matsuda, Toshiyuki Ishiwata, and Zenya Naito from Departments of Pathology and Integrative Oncological Pathology, Nippon Medical School, for their helpful discussions.