Clear cell hidradenoma: a mimic of metastatic clear cell tumors.

Clear cell hidradenoma is a benign skin appendage tumor that may mimic conventional-type renal cell carcinoma. Histologically, clear cell hidradenoma contains small ductular lumens, focal apocrine and squamoid change, and a less prominent vascular pattern than renal cell carcinoma. Furthermore, immunohistochemical studies can aid in distinguishing the 2 tumors. Knowing the cytologic features of primary skin adnexal neoplasms helps distinguish them from cutaneous metastases, which are more commonly referred for fine-needle aspiration biopsy evaluation. Detailed clinical history, physical findings, and ancillary studies are essential for correct diagnosis and categorization of these tumors. We report the rare case of a patient with renal cell carcinoma who underwent excision of an axillary clear cell hidradenoma, which was clinically suggestive of cutaneous metastatic disease.