Complex Mammary Adenoma with Sebaceous Differentiation in a Dog.

Summary: Sebaceous metaplasia arising within a complex adenoma of the left fourth mammary gland is described in a 9-year-old miniature pinscher bitch. Microscopically, the tumour was composed of tubular and ductular structures admixed with clusters of spindle-shaped, myoepithelial-like cells and units formed of well-differentiated sebocytes surrounded by basaloid cells. Abundant lipid droplets were identified within the latter population by Sudan III staining. Immunohistochemical expression of cytokeratin AE1/AE3 was detected in epithelial cells and in the cells with sebaceous differentiation. [ABSTRACT FROM AUTHOR]