Lactalbumin-positive mammary carcinoma in a mare

Development and Pathology of the Equine Mammary Gland

An understanding of the anatomy, histology, and development of the equine mammary gland underpins study of the pathology of diseases including galactorrhoea, agalactia, mastitis, and mammary tumour development. This review examines the prenatal development of the equine mammary gland and the striking degree to which the tissue undergoes postnatal development associated with the reproductive cycle. The gland is characterised by epithelial structures arranged in terminal duct lobular units, similar to those of the human breast, supported by distinct zones of intra- and interlobular collagenous stroma. Mastitis and mammary carcinomas are two of the most frequently described equine mammary pathologies and have an overlap in associated clinical signs. Mastitis is most frequently associated with bacterial aetiologies, particularly Streptococcus spp., and knowledge of the process of post-lactational regression can be applied to preventative husbandry strategies. Equine mammary tumours are rare and carry a poor prognosis in many cases. Recent studies have used mammosphere assays to reveal novel insights into the identification and potential behaviour of mammary stem/progenitor cell populations. These suggest that mammospheres derived from equine cells have different growth dynamics compared to those from other species. In parallel with studying the equine mammary gland in order to advance knowledge of equine mammary disease at the interface of basic and clinical science, there is a need to better understand equine lactational biology. This is driven in part by the recognition of the potential value of horse and donkey milk for human consumption, particularly donkey milk in children with 'Cow Milk Protein Allergy'.

Case Report of a Mare Diagnosed with a Metastatic Mammary Carcinoma after the Excision of a Recurrent Intraocular Neuroepithelial Tumor

Simple Summary

This case report describes the unusual presentation of two rare tumors in a mare diagnosed over a short period of time (9 months), affecting the eye and the mammary gland, with a relapse of the ocular tumor presenting histological features that cannot be attributed to any specific neoplastic entity. In the study, we describe the in vivo diagnosis and treatment of the neuroepithelial intraocular tumor and the post mortem detection of a metastatic malignant mammary carcinoma.

Abstract

A 24-year-old Irish Cob mare was presented with a peripheral iris mass, which was surgically resected and diagnosed as an undifferentiated neuroepithelial tumor. A few months later, a relapse occurred with histological features characterized by a more solid appearance and squamous differentiation. Subsequently, the mare was presented with rapidly spreading multiple subcutaneous masses and, at the onset of neurological signs, was humanely euthanized and subjected to a complete post mortem examination. The necropsy confirmed the presence of numerous widespread masses in the subcutaneous tissue, several internal organs, and mammary gland. Histological and immunohistochemical (IHC) examinations were performed on all masses, allowing the diagnosis of mammary carcinoma with several visceral and subcutaneous metastases. Considering the post mortem findings, the second intraocular mass was submitted to histological and IHC re-evaluation to differentiate it from an intraocular metastasis of the mammary carcinoma. The results of the histological and IHC analyses confirmed the diagnosis of neuroepithelial tumor relapse. This is the first case of a metastatic mammary carcinoma concurrent with a recurrent intraocular neuroepithelial tumor in a mare. This case was a challenge for both clinicians and pathologists involved and highlighted the importance of post mortem and IHC evaluations.

Bovine mammary progenitor cells: current concepts and future directions

Although cell number is positively correlated with milk production, much remains to be learned about the bovine mammary stem cell and progenitor cells. Bovine mammary development is driven by many of the same classic mammogenic hormones studied in murine models, yet histologic features of bovine mammary development differ from that of rodent models. Most notably, terminal end buds, as they have been described for murine models, do not exist in the bovine mammary gland. However, among the most important common features of mammary development in disparate species is the involvement of histologically distinct, lightly staining epithelial cells as putative stem and progenitor cells. Although stem cell research has often focused on mammary development, mammary stem cells seemingly provide the basis for mammary growth and cell turnover in the mature animal. These cells provide an obvious focus for research aimed at increasing the efficiency of milk production. This review addresses recent findings concerning the histology and molecular physiology of putative bovine mammary stem and progenitor cell populations, areas where more study is critically needed, and areas where studies of bovine mammary physiology may present a unique opportunity to better understand mammary physiology in many species.

Invasive ductal carcinoma of the mammary gland in a mare

A 21-year-old thoroughbred mare had a 35 x 14 x 10 cm mass involving the mammary gland. Metastases were found in the kidneys, lungs, skeletal muscles, and regional lymph nodes. Histopathologic examination of the tumor revealed a ductal solid carcinoma with extensive intraductal and intralobular involvement and focal infiltration of the adjacent stroma. The intralobular neoplasms were divided into irregularly shaped islands and sheets of polygonal and spindle-shaped epithelial cells by thick or thin fibrous connective tissue bundles. The neoplastic cells had a small or moderate amount of cytoplasm that stained faintly with eosin and round or oval hyperchromatic nuclei. Immunohistochemically, the neoplastic cells were strongly positive for Lu-5, weakly positive for AE1/AE3, vimentin, and glial fibrillary acidic protein, and negative for cytokeratin 8, cytokeratin 14, alpha-smooth muscle actin, calponin, and S100. The neoplasm was diagnosed as an invasive ductal carcinoma of the mammary gland with multiple metastases.