Keratoacanthoma versus squamous-cell carcinoma.

Keratoacanthoma is a skin tumor which after a period of rapid growth spontaneously involutes. It has certain clinical and histologic similarities to a low-grade squamous-cell carcinoma. It has been defined accurately in numerous papers, 1-6 which contain a complete review of the literature. In these it appears as a benign tumor which, as such, lacks the tendency to progress that characterizes malignant growths. The close resemblance between keratoacanthoma and the "button" type of squamous-cell carcinoma makes clinical distinction between them difficult or impossible. During this study it became apparent that distinction is possible on pathologic grounds, even in early keratoacanthoma. Confusion between the two conditions has occurred previously in the experience of one of us (Montgomery) (Fig. l a ). This study was intended to furnish reliable criteria of differentiation between