In a review of 335 cases of keratoacanthomas, there is a continuous histologic spectrum from lesions which are cytologically benign to those which are cytologically carcinomas. Histologically, an abnormal clone of epidermal cells is often present adjacent to an actinic keratoacanthoma. It is proposed that the normal epidermis, the epithelium forming the acral portions of the skin appendages, and an abnormal clone of epidermal cells participate as a unit in the formation of an actinic keratoacanthoma. The contribution made by normal clones of cells from skin appendages and possibly from the epidermis is a feature of keratoacanthoma which distinguishes it from squamous cell carcinoma. The differentiation between actinic keratoacanthomas and squamous cell carcinomas is biologic rather than histologic. Evidence that carcinoma-like keratoacanthomas always spontaneously regress is lacking.
Reed RJ. Actinic Keratoacanthoma. Arch Dermatol. 1972;106(6):858-864. doi:10.1001/archderm.1972.01620150044015