Case Report: Two cases of mammary intraductal papillary adenomas in nulliparous aged dairy cattle

Despite the mammary gland’s extended volume, intense metabolic turnover and economic importance in dairy cattle, it is a mystery why mammary neoplasms are so rare in this species. This report describes the gross, histopathological, and immunohistochemical features of two cases of mammary intraductal papillary adenomas in two, nine- and 10-year-old, nulliparous Holstein–Friesian cows that were part of a long-term experiment concerning bovine spongiform encephalopathy (BSE). Necropsy revealed multiple intraductal papillary masses and ductal accumulation of serous fluid and / or suppurative exudate, confined to one mammary quarter in each cow. Microscopically, lesions consisted of well-differentiated papillary proliferations lined by cytokeratin-positive epithelial cells supported by smooth muscle actin–positive myoepithelium and vimentin-positive fibrovascular stroma. A periodic acid–Schiff reaction confirmed an intact basal membrane. No necrosis, invasive growth or metastasis were detected. This case report of two benign mammary neoplasms in aged, nulliparous dairy cows provides empirical evidence for the hypothesis of parity- and lactation-related protection from neoplasia in cattle.