Bronchogenic adenocarcinoma in a cat: an unusual case of metastasis to the skin.

A 6-year-old, spayed, female, domestic shorthair cat was presented for decreased activity. A nodular lesion was found in the skin extending into the subcutaneous tissue of the right abdominal flank. On lateral and ventrodorsal radiographs of the thorax, an opacity involving the entire right caudal lung lobe and pleural effusion were noted. Cytologic evaluation of cells in the thoracic fluid and in the mass revealed a population of atypical epipthelial cells with marked anisocytosis and high N:C ratios, organized in acinar-like clusters. Multinucleated cells and several mitotic figures were found. The cytologic interpretation was carcinoma. Because of the progressive severity of clinical signs, the cat was euthanized. Histologic evaluation of tissues obtained at necropsy indicated a bronchogenic adenocarcinoma in the lung, with metastasis to the skin of the right flank, but no involvement of the digits. Based on immunohistochemical stains, the neoplastic cells strongly co-expressed cytokeratin and vimentin, and were negative for S-100 and actin-specific antigen. Bronchogenic adenocarcinoma is an uncommon neoplasm in cats, and the digits are the most common sites of metastasis. This case was unusual in that the skin of the abdominal wall was the primary site of metastasis, with no involvement of the digits.