Primary Solid Pulmonary Adenocarcinoma in a dog

Background: In veterinary medicine, although primary lung tumors are rare compared to metastatic malignant neoplasms, an increase in the number of primary lung tumors in dogs has been reported in the past decades. Consequently, identifying epidemiological, clinical, and pathological features of these neoplasms is essential for early and precise diagnosis. This paper aimed to report a case of a non-metastatic primary solid pulmonary adenocarcinoma in a dog and review the clinical, pathological, and immunohistochemical aspects of this neoplasm.Case: An 8-year-old female Cocker Spaniel was admitted to the Small Animals Veterinary Hospital of the Rural Federal University of Rio de Janeiro (Brazil) with a history of progressive weight loss and clinical dyspnea. Physical examination revealed the following: body temperature, 38.7ºC; capillary refill time, one second; heart rate, 104 beats/min; respiratory rate, 40 breaths/min; pallor mucosa; blood glucose, 133 mg/dL; and body score, 2 (1-9). A thoracic radiograph revealed a diffuse radiopaque pattern of the pulmonary parenchyma, pleural effusion, and a large mass that extended through both hemithoraces. An ultrasound-guided cytological examination was performed and displayed moderate cellularity in a bloody background. Cells presented distinct cell borders, large bluish cytoplasm, round hyperchromatic or vesicular nuclei, and evident nucleoli. Three months after the first clinical consultation, the dog’s state kept deteriorating and the owner opted for the euthanasia. Autopsy of the lungs showed multiple, poorly defined, coalescent nodules with an average size of 20.0×15.0×10.0 cm. The nodules occupied roughly 70% of the pulmonary parenchyma, including right and left cranial lobes, medium lobe, and a large portion of the caudal lobe. The cross-sections of the tumors were multinodular, soft, and white. Cystic areas filled with bloody exudates were also found within the tumor. Representative tissue samples were fixed in 10% formalin, processed routinely, and stained with Hematoxylin and Eosin. Fragments from the lung tumor were submitted for immunohistochemistry evaluation with primary antibodies anti-CK pan, anti-CK7, anti-CK20, anti-vimentin, TTF-1, CD56, synaptophysin, and chromogranin. Microscopic examination of the tumor revealed a dense and solid monomorphic epithelial neoplastic proliferation supported by a thin and scant fibrovascular stroma. Cells presented distinct cell borders, a slightly granular eosinophilic cytoplasm, hyperchromatic, round, and vesicular nuclei, evident nucleoli, and numerous mitoses. Necrotic areas were also observed scattered in the tumor. Immunohistochemically the cells expressed CK pan and CK7 but failed to express immunoreactivity to vimentin, CK20, TTF-1, CD56, synaptophysin, and chromogranin. The morphological and immunohistochemical features were consistent with a primary lung tumor, and hence, classified as a solid adenocarcinoma.Discussion: The solid pattern of primary lung adenocarcinomas is uncommon in domestic animals. Assessment of morphological features and immunohistochemical evaluation are essential for the definitive diagnosis of primary pulmonary neoplasms. Due to the increased number of primary pulmonary tumors reported in dogs in the last few decades, primary pulmonary neoplasms should be considered in the differential diagnosis of pulmonary masses, especially when there is no evidence of tumors elsewhere in the body