Mammary adenoma with sebaceous differentiation in a dog

Atypical canine mammary adenoma characterized by cystic ducts comprising a single layer of basaloid cells with myoepithelial differentiation

This report describes an atypical mammary adenoma with a rare histological feature characterized by proliferating single-layered cystic ducts composed of basaloid cells with frequent myoepithelial differentiation. A 9-year-old, intact female Miniature Pinscher dog had mammary tumors on the thorax. Histologically, one of tumors comprised the proliferation of two types of tubular structures; the single-layered cystic ducts lined by flattened cells and double-layered tubules with luminal cells and outer spindle cells. The former ducts were predominant in the tumor and contained pale basophilic mucus, which was Alcian blue (pH 2.5)-positive, but periodic acid Schiff-negative. Immunohistochemical staining indicated that the cells lining single-layered cystic ducts were negative for the luminal epithelial marker, cytokeratin (CK) CAM5.2, but were constantly positive for basal cell markers CK14 and p63 and frequently positive for SMA. Electron microscopy revealed fine, parallel myofilaments within these single-layered neoplastic cells. These histological and immunohistological examinations suggested that the origin of the tumor was bipotential mammary progenitor cells with predominant differentiation into the myoepithelial progenitor linage.

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, andαSMA 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.