Amelanotic ocular melanoma with lung metastasis in a domestic rabbit (Oryctolagus cuniculus)

ABSTRACT: Uterine adenocarcinoma and lymphoma are among the most diagnosed neoplasms in rabbits. Melanomas have also been reported in rabbits; however, they occur less frequently. A domestic rabbit (Oryctolagus cuniculus) was referred to for veterinary care due to an increase in ocular volume. Ophthalmic evaluation revealed buphthalmos of the left eye, conjunctivitis, corneal neovascularization, superficial ulcerative keratitis, and the presence of an intraocular mass. The patient underwent an enucleation procedure, and the ocular bulb was sent for histopathological evaluation. Five days after the surgery, the patient died and was sent for postmortem examination. Macroscopic examination of the ocular bulb revealed a firm whitish mass in the choroid in the uveal region upon sectioning. In the lungs, whitish, firm, multifocal to coalescent nodules, randomly distributed, were observed, measuring approximately 6 mm in diameter. Histological evaluation of the ocular bulb revealed a mesenchymal neoplastic proliferation, highly cellular, non-limited, non-encapsulated, with invasive growth. In the lung, a dense neoplastic proliferation of elongated and sometimes round cells was observed, densely cellular, poorly demarcated, infiltrative, and non-encapsulated appearance. Sections were subjected to Fontana Masson staining and immunohistochemical examination with the Melan-A antibody, showing positive staining. Based on microscopic, histochemical, and immunohistochemical characteristics, the diagnosis was intraocular amelanotic melanoma with metastasis to the lung.