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Keratoacanthoma is a common epithelial tumor of the skin characterized by rapid growth, histopathologic features similar to those of cutaneous squamous cell carcinoma, and a certain tendency toward spontaneous regression. The exact nosology and classification of keratoacanthoma are still a matter of debate. Some authors regard keratoacanthoma as a benign cutaneous tumor that is the prototype of a “pseudomalignant” tumor of the skin, whereas others maintain that it is a malignant neoplasm and should be regarded as a variant of cutaneous squamous cell carcinoma.
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The first description of solitary keratoacanthoma was provided by Sir Jonathan Hutchinson in 1889, who called this tumor “crateriform ulcer of the face.”1 The term keratoacanthoma was officially first adopted in 1950 by Rook and Whimster.2 In addition to the solitary type of keratoacanthoma, a number of other variants have been described in the literature. Ferguson–Smith, in 1934, reported on a young patient presenting with multiple self-healing squamous cell carcinomas of the skin, a condition that later would be renamed as “multiple keratoacanthomas of the Ferguson–Smith type.”3 The occurrence of hundreds or even thousands of lesions in a single patient, today known as “multiple keratoacanthomas of the Grzybowski type,” was reported by Grzybowski in 1950.4 In 1961, Fisher published the first report on digital keratoacanthoma, pointing at the destructive features of the disease.5 Another rare variant, today described as “keratoacanthoma centrifugum marginatum,” a term that was coined in 1962 by Miedzinski and Kozakiewicz,6 was first described by Puente Duany in 1958.7
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The exact incidence of keratoacanthoma is unknown. The tumor is more frequent in light-skinned persons, and rarer in dark-skinned and Japanese persons. The relative frequency in comparison with squamous cell carcinoma of the skin is controversial, but most studies show a lower incidence of keratoacanthoma than of squamous cell carcinoma. Discordant results may be explained, at least in part, by differences in classification of these lesions.
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Studies on gender distribution reveal that both sexes are affected equally, possibly with a slight predilection for men. Keratoacanthoma occurs mostly in adult life, with a peak between the ages of 55 and 65 years; it has been observed rarely in younger patients. The familial type of keratoacanthoma occurs often during adolescence, and a neonatal case has been reported.8 Although the incidence was thought to remain stable ...