Equine conjunctival haemangiosarcoma: Clinical presentation, management, and outcome of seven cases in the United Kingdom.

Background: Only 27 cases of equine conjunctival haemangiosarcoma have been reported in the literature over the past 37 years. Out of these, 22% of cases were lost to follow-up, 52% were euthanized, and 26% survived. A scarcity of cases and information is available for this rarely seen conjunctival tumour. Aim: To describe the clinical features, management, and outcome of conjunctival hemangiosarcoma in seven horses in the UK. Methods: Optivet medical records were reviewed for equine cases seen or advised on with a histopathological diagnosis of conjunctival haemangiosarcoma between January 2013 and March 2023. Medical records were accessed for details of signalment, history, management, and follow-up. Histopathology was used to confirm the diagnosis of haemangiosarcoma and assess the surgical margins. Immunohistochemistry was performed in a minority of cases with poorly differentiated solid tumours to support vascular lineage. Results: Seven eyes from seven horses (five geldings and two mares) with a mean age of 16 years and median of 18 years (range 10-21 years) met the criteria. Serosanguinous discharge was seen in six eyes. All eyes were managed surgically; 4 by exenteration and 3 by conjunctivectomy/keratectomy. Adjunctive cryotherapy was performed in two eyes. Metastatic disease in the ipsilateral parotid salivary gland, confirmed with histopathology, was seen in one horse. Surgical margins were clear in all but one eye. Solar elastosis was noted in five eyes. All horses were healthy at the last follow-up (0.2-5 years, mean 2.9 years, and median 2 years). Conclusion: Equine conjunctival haemangiosarcoma is rare. Serosanguinous ocular discharge is a common clinical sign. Early surgical excision is highly effective. Solar elastosis is a common histopathological feature, suggesting a role for UV-light in the pathogenesis.