Bronchioloalveolar Carcinoma in an Aged Beagle Dog

A pulmonary mass was observed in a 16-year-old beagle dog. In the histopathology, a well-circumscribed mass composed of cuboidal to low or tall columnar neoplastic cells proliferating in a papillary, acinar or solid pattern and abundant cholesterin deposition was observed. The tumor cells had eosinophilic to abundant clear or foamy cytoplasms. The cells were arranged around blood vessels with the nuclei at the periphery of the cells in a pseudo-rosette formation, especially in the tall columnar cells. In the immunohistochemistry, the neoplastic cells were positive for cytokeratin and surfactant apoprotein A, but not for vimentin and chromogranin A. In the electron microscopy, numerous vacuoles ranging from 0.5 to 2 μm in diameter were observed in the basal part of the neoplastic cells and some of these vacuoles contained myelin-like materials. These findings indicate that these neoplastic cells were derived from alveolar type II cells. Therefore, the pulmonary mass was diagnosed as bronchioloalveolar carcinoma.