Keratoacanthoma within a superficial spreading malignant melanoma in situ.

A case of a keratoacanthoma arising from the center of a superficial spreading malignant melanoma in situ is presented. The keratoacanthoma already showed regressive changes in its central area, and the superficial spreading malignant melanoma had partially disappeared at the site in which the keratoacanthoma had arisen. The possible mechanisms of these interactions are discussed.