Squamoid eccrine ductal carcinoma of the scalp.

Squamoid eccrine ductal carcinoma (SEDC) is an exceedingly rare tumor that shows both squamous and adnexal ductal differentiation. We report a case of this unusual tumor occurring on the occiput of a 53-year-old man. A histopathological examination revealed a nodular lesion infiltrating the dermis and subcutaneous tissue with numerous duct-like structure and squamoid differentiation foci. Five months later, the patient presented with a palpable mass at the site of the previous excision and the right side of the neck. Sono-guided fine needle aspiration of the right neck mass was performed and was diagnosed as a metastastasis of a lymph node. A right neck node dissection and re-excision of the occiput was performed. The histopathological findings were similar, but squamoid differentiation was more prominent than that in the previous lesion. Because of the rarity of SEDC, little is known about its biological behavior and optimal treatment.