Surgical treatment of a mammary gland comedocarcinoma in an Arabian mare: Post‐operative management, and histopathological and immunohistochemical features

Abstract

A lactating 20-year-old, brown, Arabian mare, weighing about 300 kg, presented for bleeding from one teat and severe swelling of the entire mammary gland. The mare had untreated mastitis 10 months before. Consequently, a gangrenous teat developed after chronic bloody and purulent discharges. The teat was removed surgically by the field veterinarian. At that time, the mammary gland increased in size. Bloody and purulent discharges restarted 10 days previously. Under general anaesthesia, the entire mammary gland was removed. Comedocarcinoma was diagnosed by histopathological assessment. Immunohistochemical staining was performed for pan-cytokeratin and vimentin. Microscopic examination of immunohistochemical stained slides revealed expression of pan-cytokeratin. In conclusion, this report describes clinical, macroscopic, histopathological and immunohistochemical characteristics of comedocarcinoma that did not metastasise to regional lymph nodes. Reports in the field of equine oncology contribute to improved general knowledge in equine medicine, contributing to better diagnosis and treatment.

Development and Pathology of the Equine Mammary Gland

“…A full-term birth at an early age and prolonged breast feeding both confer protective effects, whereas pregnancy and involution are periods associated with an increased risk of tumour development [126]. At least three pregnant mares with concurrent mammary neoplasia have been reported [127,128] and recently a lactating mare that was presented with a mammary comedocarcinoma has been described [129]. Similar to the situation with laterality, no conclusions can currently be drawn regarding impact of mare reproductive history on mammary tumour development.…”

The known unknowns of equine mammary neoplasia

“…In the mare, clinical distinction between mastitis and mammary neoplasia may be difficult (Reppas et al 1996;Kato et al 1998;Hirayama et al 2003;Shank 2009;Hughes et al 2015;Sabiza et al 2021). Indeed, it has been suggested that horse owners and those caring for horses may associate any form of mammary gland enlargement with mastitis (Canisso et al 2021).…”

“…A specific framework for phenotyping equine mammary tumours is yet to be established (Sysel et al 1993;Shank 2009). In the associated clinical report, a radical mastectomy was undertaken and subsequently histological sections from the mass were examined (Sabiza et al 2021).…”

“…Whilst the broad framework may be helpful, parameters, and cut-off points for numerical values such as mitotic count, are likely to require modification in order to offer optimum prognostic value. As noted, currently no such grading framework exists for mammary tumours arising in mares (Sabiza et al 2021). In addition to morphological assessment, expression of molecular markers may be evaluated in tissue sections to guide prognostication.…”

“…Primary equine mammary tumours are rare entities that are considered to have a poor prognosis (Shank 2009). In the case report associated with this clinical commentary, the authors describe the clinical presentation, management and histopathological assessment of a comedocarcinoma arising in the mammary gland of a 20-year-old Arabian mare (Sabiza et al 2021). In their article, the authors allude to some of the challenges of diagnosis and prognostication in cases of equine mammary neoplasia.…”