Pulmonary Adenocarcinoma with Cutaneous Metastasis in a Dog

Simple Summary Primary lung cancer is rare in dogs and the prognosis can often be poor. In this report, we describe the post-mortem evaluation of a dog with a single large mass in one lobe of the lung, numerous smaller masses spread throughout the other lobes, and a single skin mass on the chest. Histopathological examination of the lung samples revealed multiple proliferations of neoplastic epithelial cells, with some showing microvilli-like structures on their luminal cytoplasmic edges. Histopathological examination of the skin mass revealed neoplastic cells that closely resembled those seen in the lung. Electron microscopy of the skin samples showed cells resembling the respiratory epithelium, along with cells exhibiting microvilli, which are indicative of cilia. The diagnosis was pulmonary adenocarcinoma with cutaneous metastasis, and this is the first report of a dog with lung cancer metastasizing to the skin.Abstract Primary lung cancer is rare in dogs and depending on the tumour stage and subtype, the prognosis can be poor. In this report, we describe a 10 year-old female intact Yorkshire terrier that presented progressive weight loss and chronic pain of unknown origin. Due to the poor condition of the dog, it was subsequently euthanized. Post-mortem evaluation revealed a single large mass in the left caudal lung lobe, with numerous pale, proliferative lesions of various sizes dispersed throughout all the lobes. Additionally, a solitary skin mass was palpated on the mid-thoracic body wall. Histopathological examination of the lung samples revealed multiple distinct, non-encapsulated, expansive neoplastic epithelial cell proliferations with dense cellularity, exhibiting growth patterns, ranging from papillary to micropapillary to solid, accompanied by central areas of necrosis. In some areas, microvilli-like structures were observed on the luminal cytoplasmic margins of the neoplastic cells. The histopathology of the skin mass closely resembled that of the lung. Electron microscopy of the skin samples revealed regions containing cells resembling the respiratory epithelium, along with cells exhibiting processes or microvilli indicative of cilia. The diagnosis was pulmonary adenocarcinoma with cutaneous metastasis. This is the first report of a canine with primary lung cancer that metastasized to the skin.