Keratoacanthoma clinical behavior: a systematic review.

As of 2013, keratoacanthomas (KAs) have not been decided on as either a benign or a malignant entity. Originally considered benign epidermal growths, the assertion by Hodak, Jones, and Ackerman that these lesions are truly "an expression of squamous cell carcinoma" (SCC) fueled the controversy and placed some of the biggest names in the field on opposite sides of the issue. Without a clear understanding of the etiology of KAs and without stringent diagnostic criteria, the literature in regard to KA contains scant reports of their "metastatic potential." Four hundred forty-five cases of KA with reported follow-up and outcomes were reviewed from 113 published articles. In our data set, none of these cases resulted in death or distant metastases. When compared with 429 cases of SCC of the skin, with 61 cases of metastases and 24 deaths as a direct result of SCC, the biologic behavior of the 2 entities is distinct and evident. KAs are benign epidermal growths and not a malignant variant of SCC.