MELANOMA METASTÁTICO SEM FOCO PRIMÁRIO IDENTIFICÁVEL EM UM CÃO FILA BRASILEIRO – RELATO DE CASO E REVISÃO DE LITERATURA

Abstract

Melanomas are malignant neoplasms originating from melanocytes and are often diagnosed on the skin of dogs. Often the lung is metastasized to several tumors, however, the occurrence of melanoma primarily in the lung without apparent cutaneous focus is rare in the canine species. The aim of this study is to describe a case of lung melanoma with no identifiable primary focus in a dog. It is a 10-year-old Fila Brasileiro dog, attended at the Veterinary Hospital of the Federal University of Paraíba with a history of apathy, anorexia and weight loss for 30 days. The animal was submitted to pulmonary X-ray, abdominal ultrasonography and thoracotomy, by which an irregular black mass involving the lung and mediastinum was identified. Given the patient's clinical condition and unfavorable prognosis, the animal was referred to euthanasia and subsequent necropsy and histopathological evaluation. The macroscopic findings revealed a firm, black mass, forming multifocal nodules that, in general, protruded from the pulmonary pleural surface and extended to the mediastinum. Fragments of organs of the cavities were referred to histopathology for routine staining with hematoxylin and eosin and an expansive and infiltrative mass consisting of pleomorphic melanocytes, forming nests, associated with intra- and extracellular melanin, was scattered throughout the lung parenchyma. No changes were observed in the other tissues evaluated. The diagnosis of melanoma was established based on the clinical and pathological findings, being confirmed by means of histopathology. Melanomas are melanocytic tumors commonly seen on the skin of dogs and may metastasize to organs such as the lung and lymph nodes, however, foci in cavity organs with no apparent cutaneous nodules are rare in the canine species. There are descriptions of congenital melanomas in production species, however they are observed in still young animals. Primary melanomas are described in the larynx in human chronic smoking patients, however there is no well-defined mechanism for its occurrence in canine patients. Melanomas are important neoplasms of dogs and their occurrence without apparent primary focus should be better studied in order to understand factors predisposing to their occurrence and should be included in the differential diagnosis of lung and metastatic neoplasms.