Apocrine ductular adenoma in a cat
History: Skin biopsy from a 15 year-old cat, taken from the abdomen.
Haired skin: The dermis contains a multilobulated, well circumscribed,unencapsulated neoplasm of epithelial cells arranged in a tubulo-papillary pattern in an abundant collagenous stroma and occasionally forming dilated cystic structures filled with homogenous eosinophilic material.Neoplastic cells covering papillary structures and lining ducts are often distinctly bilayered with scant eosinophilic cytoplasm and indistinct cellborders. Nuclei are oval with coarsely stippled chromatin. There are 5 mitotic figures in 10 400x fields. The neoplasm appears to have been completely excised. There is a focal area of necrosis containg numerous cholesterol clefts, and there are multifocal aggregates of lymphocytes inthe interstitium.
Based on the location we considered a mammary gland as the origin of the neoplasm, but since we did not see normal mammary tissue in the biopsy a peri-follicular apocrine gland is a likely possibility. Both are “apocrine glands” and form similar neoplasms. The double-layer of epithelial cells are characteristic of ductular neoplasms rather than neoplasms arising from the glandular cells.