Equine orbital neoplasia: a review of 10 cases (1983-1998).

The clinical manifestations, laboratory findings, and survival times of 10 horses with orbital neoplasms are reported. In all cases, orbital neoplasms were malignant and locally invasive with no defined surgical circumscribed edges. It was often difficult to identify the primary cell type of the neoplasia in histologic specimens due to the poorly differentiated, anaplastic nature of the majority of cases. All except one horse were eventually euthanized 2 mo to 5 y after diagnosis due to poor response to treatment, metastasis, or unrelenting orbital neoplasia. Mean survival time increased with surgical treatment, but no significant difference was found among no treatment, chemotherapy, surgical mass removal, or exenteration/enucleation. Equine practitioners should be aware of the marked difference in prognosis of orbital neoplasms compared with ocular or localized eyelid neoplasia.