EXPRESS: Pulmonary epithelial-myoepithelial carcinoma with high-grade transformation in a cat

Case Summary A 14-year-old spayed female Scottish Fold cat was presented to a private veterinary clinic for a health check. Radiography revealed a nodule measuring 1.0 cm diameter in the cranial segment of the cranial lobe of the left lung. On day 12, non-contrast-enhanced computed tomography revealed a well-defined pulmonary nodule measuring 1.7 cm in diameter in the same area. On day 48, the nodule in the cranial segment of the left cranial lobe was resented by lobectomy. The nodule was firm and pale pink in surface color. Microscopically, the mass was adjacent to the bronchi and bronchial glands, and was composed of luminal cells forming the duct structure and an outer layer of non-luminal cells with squamoid differentiation. Tumor cells partially invaded into the surrounding parenchyma. Immunohistochemically, the luminal cells were positive for CK AE1/AE3, CK7, CK19, TTF-1 and HER2. Non-luminal cells were positive for CK AE1/AE3, p63, calponin, SMA and p40. The Ki-67 indices of the luminal and non-luminal cells were 10.4% and 12.8%, respectively. Based on these findings, the tumor was diagnosed as a pulmonary epithelial-myoepithelial carcinoma with high-grade transformation as defined in the human WHO classification. Relevance and novel information This is the first report of pulmonary epithelial-myoepithelial carcinoma with high-grade transformation, characterized by morphology and immunohistochemistry.