Cutaneous clear cell adnexal carcinoma in two dogs: cytological and immunohistochemical evaluation

In this study, cases of cutaneous clear cell adnexal carcinoma were diagnosed on the right forepaw of a 6-year-old female dog and on the right hind paw of an 8-year-old male dog. On the cytological examination, scattered cell groups were seen on the hemorrhagic background, whose cytoplasmic borders could hardly be distinguished. Although the cells showed marked pleomorphism but were generally oval, round, or spindle-shaped. Anisokaryosis, karyomegaly, and one or more prominent nucleoli were noted in the nuclei. Pseudoinclusions were found in some cell nuclei. Histologically, it was centrally necrotic, expansive growth consisting of lobular areas in the dermis. The neoplastic cells consisted of oval round-shaped epithelioid cells with clear cytoplasm showing marked anisocytosis, anisorkaryosis and karyomegally. Nuclei were oval or round in shape with prominent nucleoli. Cystic changes and calcified areas in layers (psammoma bodies) were noted in these areas. Few mitoses were found. In the immunohistochemical examination, tumor cells were positive for vimentin, S-100, MART1 (Melan A), and cytokeratin (MNF116) and negative for glial fibrillary acidic protein (GFAP) and smooth muscle actin (SMA). Based on these findings and results, the tumors were diagnosed as canine clear cell adnexal carcinoma. According to the literature review, this is the first case in which we found psammoma bodies and nuclear pseudo inclusions on microscopic examination of canine cutaneous clear cell adnexal carcinoma.