Keratoacanthoma : Controversies
Keratoacanthoma has been the subject of numerous controversies with regards to its pathogenesis and behavior. It has been called a benign tumor, a pseudomalignancy, a regressing malignancy, or a distinct variant of squamous cell carcinoma. Most cases undergo spontaneous regression after a period of rapid growth; however, some tumors grow slowly or don't regress. There are well-documented cases showing invasion of underlying skeletal muscle, perineural invasion, or vascular invasion yet no tendency to metastasize. On the other hand, some cases with classic clinical and histologic features of keratoacanthoma show recurrence or metastatic spread. From clinical standpoint, keratoacanthoma is best regarded as a distinct subtype of squamous cell carcinoma. Perhaps it represents the most well-behaved end of the spectrum of squamous cell carcinomas.