A keratoacanthoma (KA) is a unique lesion with a characteristic clinical appearance. There is controversy about the benign versus malignant nature of this lesion. A KA resembles an SCC histologically; consequently some dermatologists and dermatopathologists consider it to be a low-grade variant of an SCC and believe that it should be treated as such. Lesions may be clinically impossible to differentiate from SCCs.

KAs generally occur in persons older than 65 years of age.

If ignored, some KAs have been reported to regress spontaneously. This fact lends support to the theory that this lesion is benign in nature.

Lesions arise quickly, usually developing in 3 to 4 weeks.

Spontaneous regression may result in a small depressed scar.

A KA usually occurs as a single, dome-shaped, erythematous or skin-colored nodule with a central keratin core (central crater) with an overlying crust (Figs. 31.20 and 31.21). It resembles the appearance of a volcano.

It generally attains a diameter of 1.0 to 2.5 cm.

An excisional or incisional biopsy is often recommended so that the complete architecture of the lesion can be evaluated histologically. An insufficient biopsy, such as a shave biopsy, may result in a histology that is indistinguishable from an SCC.

When KAs appear on areas where it is difficult to perform an excisional biopsy, such as the nose and external ears, a deep shave biopsy is often adequate to obtain sufficient tissue.

As with the nonmelanoma skin cancers such as BCC and SCC, lesions tend to appear on the sun-exposed areas of the face, ears, neck, dorsa of hands, and forearms.