Sebaceous adenoma with a cutaneous horn.

Cutaneous horns are common lesions that usually represent actinic keratoses, verrucae, seborrheic keratoses, and squamous cell carcinomas. We present a remarkable example of a sebaceous adenoma with cutaneous horn formation. The solitary lesion occurred over the left clavicle of a 71-year-old man without evidence of the Muir-Torre syndrome. There have been only three previous reports of sebaceous tumors (one sebaceous adenoma and two sebaceous carcinomas) producing cutaneous horns, the latter of which are actually pseudohorns, exophytic extensions of tumor without hyperkeratosis.