Mammary tubulopapillary carcinoma in a mare, requiring bilateral mastectomy.

Abstract

Mammary neoplasia is uncommon in the mare and often mistaken for mastitis (Reppas et al. 1996). Incidence rates of mammary tumours in horses of 0.1–1.9% are reported, with carcinomas the most common (Brito et al. 2008). Due to the low incidence, and similarity of initial signs to those of mastitis, diagnosis is often delayed until after antibiotic and antiinflammatory treatment has failed (Boyce and Goodwin 2017). Mares are often, therefore, presented in an advanced stage of disease with a poor prognosis (Ferreira Júnior et al. 2019). Due to the infrequency of mammary neoplasia in horses it has been difficult to develop an evidence based approach to treatment. Studies in domestic animals report a low success rate with conservative management of these neoplasms. Combined with their highly aggressive and metastatic nature, surgical excision has been perceived as the treatment of choice in the initial management of these neoplasms (Seahorn et al. 1992). Mammary tubulopapillary carcinomas have been reported in multiple species, including horses. They are more malignant than other forms of mammary carcinoma; lymphovascular and lymph node metastasis occurs commonly (Goldschmidt et al. 2016). This case report describes the surgical treatment of a mare with advanced bilateral mammary tubulopapillary carcinoma and describes the use of a barbed wound closure device to reduce surgical dead space to aid in complete wound closure. An 18-year-old, Thoroughbred, multiparous, barren mare was presented to the referring veterinarian with an enlarged left mammary gland during a routine reproduction examination. Over the next 3 months the mare received three courses of anti-inflammatory drugs and antibiotic therapy based on culture and sensitivity, but clinical signs persisted. The left mammary gland was scanned, revealing a mass in the interstitial tissue. The mare was then referred for further investigation, 3.5 months after initial presentation. On presentation, the mare underwent a general physical examination, the results of which were within normal limits except that the left mammary gland was enlarged and firm, with three ulcerative lesions (Figure 1A). No pain response was elicited upon palpation. The teat was also firm and enlarged. Palpation of the right gland revealed some firm masses throughout, with a normal teat. Serosanguinous secretions were easily expressed from each teat. A jugular blood sample was submitted for routine haematology and biochemistry (including serum amyloid A) and all parameters were within normal limits. Ultrasound examination of both glands was performed using a 2–5 MHz curved array transducer. The left gland and teat revealed extensive areas of mixed echogenicity with microlobulated margins and an abrupt interface between the mass and normal mammary tissue in some areas (Figure 1B) with more diffuse and generalised margins elsewhere. The right gland contained multiple focal areas of mixed echogenicity with microlobulated margins, and an abrupt interface between the mass and normal mammary tissue (Figure 1B). The larger focal areas were located closer to the intermammary groove, with smaller focal patches seen laterally. The right teat appeared normal. Due to the extent of the pathology in both glands, and the owner’s desire to maximise the mare’s breeding potential, the treatment elected was bilateral mastectomy. The authors acknowledge that further investigation and potential staging of any metastatic disease would have been appropriate in this case. However, these were not performed due to financial constraints of the owner and their desire to proceed to surgery irrespective of the prognosis. Prior to surgery, the mare was premedicated with 0.1 mg/kg morphine (Hameln Pharma, Hameln, Germany) and 0.04 mg/kg acepromazine (Acezine 10; Ethical Agents Ltd., Auckland, NZ) given IM, and 6.6 mg/kg gentamicin (Gentamax 100; Ceva Animal Health Ltd., Gelenorie, Australia), 4.4 mg/kg ceftiofur (Calefur 4 g; Dechra New Zealand, Paraparaumu, NZ) and 1.1 mg/kg flunixin meglumine (Colix; Randlab, Revesby, Australia) given IV. The mare was then anaesthetised routinely with 1.1 mg/kg xylazine (Xylazine 10%; PhoenixPharm, Auckland, NZ), 3.3 mg/kg ketamine (Randlab) and 0.05 mg/kg diazepam (Pamlin; CEVA) given IV, and placed in dorsal recumbency.