Malignant clear cell hidradenoma.
We report the case of a 77-year-old man with a recurrent malignant clear cell hidradenoma. Establishing histopathological criteria of malignancy for these tumors can be difficult as nuclear anaplasia may be slight to moderate or even absent; however, in contrast to the benign form, malignant clear cell hidradenoma tends to invade the surrounding tissue. As these tumors can show a high rate of local recurrence (50%) and may even metastasize to lymph nodes, bone or visceral organs, wide surgical excision should be performed after the initial diagnosis.