Keratoacanthoma: hyperplasia, benign neoplasm, or a type of squamous cell carcinoma?

Keratoacanthomas are common self limited squamous proliferations. They have been considered a benign neoplasm with involution and complete resolution within few months. Although considered the prototypical example of cutaneous pseudomalignancy, some believe that these tumors are squamous cell carcinomas and through the years there have been sporadic reports of "metastasizing keratoacanthomas". The question has been raised as to whether keratoacanthoma is an unreliable histological diagnosis or these tumors have a latent, albeit rare, malignant potential. To date, just a handful of "metastasizing keratoacanthomas" have been reported. Since a benign lesion is incapable of metastasis, some other explanation must be considered; the most likely one being a misdiagnosis. While it is clear that in some cases, the histological and cytological features of squamous cell carcinoma and keratoacanthoma are difficult to distinguish by current techniques, these occasional limitations in diagnosis do not make keratoacanthomas a carcinoma. We believe the evidence supports that keratoacanthomas are benign squamous proliferations. The diagnosis can be made with confidence in appropriate biopsies and using well established clinicopathological criteria.