Cytologic features of clear cell adnexal carcinoma in 3 dogs.

BACKGROUND: Clear cell adnexal carcinoma is a rare cutaneous adnexal neoplasm without definitive apocrine, sebaceous, or follicular differentiation. Differential diagnoses include sebaceous carcinoma, liposarcoma, and balloon cell melanoma. Immunohistochemical analysis, with positive immunoreactivity for pancytokeratin and vimentin, aids in the diagnosis. Cytologic features of clear cell adnexal carcinoma have not been described previously. OBJECTIVE: The aim of this study was to describe cytologic features of canine clear cell adnexal carcinoma. METHODS: Fine-needle aspirates (FNA) obtained prior to biopsy of cutaneous neoplasms with a histologic diagnosis of clear cell adnexal carcinoma confirmed by immunohistochemical analysis were reviewed retrospectively. Slides prepared from FNA had been stained with modified Wright-Giemsa or automated aqueous Romanowsky stain. RESULTS: Of 20 neoplasms diagnosed as clear cell adnexal carcinoma in dogs, FNA of the mass had been performed in 3 cases. Cytologic features were similar and included high cellularity, marked cellular pleomorphism, loose arrangement of neoplastic cells, and a light blue to gray background resulting from streaming of cytoplasm from ruptured cells. Neoplastic cells were oval to polygonal to spindle-shaped with wispy cytoplasmic projections. Cytoplasmic eosinophilic stippling, globular deposits, or pink needle-shaped inclusions were noted. Criteria of malignancy included marked anisocytosis, anisokaryosis and anisonucleoleosis, multinucleation, karyomegaly, macronucleoli, and atypical mitotic figures. CONCLUSIONS: Clear cell adnexal carcinoma should be included in the cytologic differential diagnosis for a canine cutaneous mass even if an epithelial origin is not readily identified owing to lack of characteristic epithelial features, such as highly cohesive cell clusters, evident cell-to-cell junctions, and distinct cytoplasmic edges.

Canine cutaneous clear cell adnexal carcinoma: histopathology, immunohistochemistry, and biologic behavior of 26 cases.

Thirty tumors including 27 distinctive cutaneous neoplasms and 3 metastatic tumors from 26 dogs were collected from diagnostic submissions to 3 laboratories. Characteristic histopathologic features included location in the subcutis or dermis (or both); lobular, nodular, and nest-like architecture; and a component of epithelioid cells with clear cytoplasm. Additional features present in most cases included follicular dermal papilla-like structures, low mitotic index, nuclear pleomorphism, necrosis, and mineralization. Cytoplasmic periodic acid Schiff-positivity, which was abolished by pretreatment with diastase, indicated the presence of glycogen in all cases. The oil red O stain did not demonstrate cytoplasmic lipid. Melanin granules, accentuated by the Fontana-Masson method, were observed infrequently. A sparsely cellular mucinous stroma and stromal cartilaginous differentiation were uncommon. By immunohistochemistry, neoplastic cells stained positively for cytokeratin (29 of 29), vimentin (28 of 28), S-100 protein (24 of 29), and melan A (8 of 12); results were negative for smooth muscle actin and calponin in all cases. Clinical follow-up information was obtained on all 26 dogs. One tumor recurred, 1 metastasized to a regional lymph node, and 1 metastasized to regional lymph nodes twice. In another case, possible pulmonary metastasis was noted radiographically. The findings are consistent with a poorly differentiated, low-grade, adnexal carcinoma of the skin. Similar canine cutaneous neoplasms have been reported as "clear-cell hidradenocarcinoma" and "follicular stem cell carcinoma." The authors propose the designation "cutaneous clear cell adnexal carcinoma."