Squamous Cell Carcinoma Developing within Lesions of Disseminated Superficial Actinic Porokeratosis.

Disseminated superficial actinic porokeratosis (DSAP) consists of multiple annular, hyperkeratotic lesions that have a bilateral distribution on sun-exposed areas, particularly the extremities. DSAPs have a wider distribution than porokeratosis of Mibelli and usually develop during the 3rd or 4th decade of life. Squamous cell carcinoma that arises in the classical type of porokeratosis of Mibelli is well-documented, but there are only a few reports of squamous cell carcinoma in DSAP. Here, we describe a 62-year-old man with DSAP who developed squamous cell carcinoma on his right forearm.