Immunohistochemical characterization of a pulmonary large-cell carcinoma in a dog

Primary pulmonary tumors are less common in dogs than secondary (metastatic) tumors. Most primary tumors are malignant and of epithelial origin. Pulmonary large-cell carcinoma is considered extremely rare in domestic animals, and some of the few reported cases actually may have been cases of malignant pulmonary histiocytosis. An 8-year-old female Wire Fox Terrier with diffuse alveolar pattern radiographically was euthanatized when it failed to respond to antibiotic therapy. Histologically, pulmonary alveolar spaces contained clusters of large round anaplastic cells with ample eosinophilic cytoplasm and large irregularly shaped nuclei with prominent nucleoli. Immunohistochemistry was used to distinguish large-cell carcinoma from malignant pulmonary histiocytosis. Tumor cells had strong immunoreactivity for cytokeratin, consistent with epithelial origin. However, a substantial percentage of the neoplastic cells co-expressed vimentin and MHC-II. The type II alveolar epithelial cell was considered the cell of origin of the neoplasm based on the presence of lamellar bodies in some neoplastic cells and immunoreactivity for surfactant protein A and thyroid transcription factor-1.