Metastasizing keratoacanthomas? The difficulties in differentiating keratoacanthomas from squamous cell carcinomas.

The problem in diagnosis of keratoacanthoma versus squamous cell carcinoma has been reviewed, and 13 patients are presented to illustrate the difficulties in differentiating between these two lesions. If the pathologist is in doubt, the lesion should be called "probable keratoacanthoma, but squamous cell carcinoma cannot be ruled out." We should all be aware that even the most careful pathologist, using all the information and material available, may still erroneously diagnose a lesion as a benign keratoacanthoma--one which, if inadequately treated, may metastasize or recur as a squamous cell carcinoma. Therefore, it is important for the clinician to treat most keratoacanthomas by adequate removal and close follow-up.