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

## TL;DR

This case report describes two rare benign mammary tumors in older dairy cows that never gave birth, supporting the idea that pregnancy and lactation may protect cows from developing such tumors.

## Contribution

The report provides empirical evidence supporting the hypothesis that parity and lactation protect dairy cattle from mammary neoplasia.

## Key findings

- Two nulliparous dairy cows had benign mammary intraductal papillary adenomas confined to one mammary quarter.
- The tumors showed well-differentiated papillary structures with intact basal membranes and no signs of invasion or metastasis.
- The findings suggest a protective effect of parity and lactation against mammary neoplasia in cattle.

## Abstract

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.