Abstract
The dog (Canis lupus familiaris) is a mammal that has been domesticated by humans for thousands of years, exhibiting great morphological and behavioral diversity resulting from processes of artificial selection. Intensive genetic selection and the development of different breeds have, however, contributed to an increased predisposition to various diseases, including dermatological and neoplastic conditions. Among the oncological conditions of importance in veterinary medicine, ocular neoplasms stand out, as they can compromise the animals’ vision, well-being, and quality of life. These neoplasms can be classified as primary, secondary, or multicentric and may affect the eyeball, the orbit, or their adnexa. Among these, eyelid neoplasms are common in dogs and may be benign or malignant. Melanocytic neoplasms originate from melanocytes and can be classified as melanocytomas or melanomas. Amelanotic melanoma presents particular diagnostic challenges due to the absence of pigmentation and may be histologically confused with other types of neoplasms. Therefore, the combination of histopathological examination and immunohistochemistry, using markers such as S-100 protein, melan-A, and vimentin, is important for diagnostic confirmation and establishing the prognosis. Treatment should be tailored according to the location and extent of the lesion, the patient’s clinical condition, and the viability of the affected eye, and may include surgical excision, cryosurgery, electrochemotherapy, and chemotherapy. The present study aims to report a case of amelanotic eyelid melanoma in a mixed-breed dog, addressing the clinical aspects, diagnosis, surgical treatment, and histopathological evaluation, as well as discussing the importance of early diagnosis and excision of the neoplasm for local control of the disease and maintenance of the patient’s quality of life.