Keratoacanthoma: Clinical and histopathologic features of regression

Background: The clinical and histopathologic features of regressing keratoacanthomas have not been adequately described in the literature. Objective: "True'' keratoacanthomas (ie, squamous tumors with evidence of spontaneous resolution) were studied clinically and histopathologically. Methods: Nineteen crateriform tumors with a partial biopsy histopathologically compatible with keratoacanthoma were followed over time for correlation with biologic behavior (ie, regression). Tumors displaying spontaneous resolution, arbitrarily defined as a decrease in size of at least 25%, were categorized as keratoacanthomas. Results: Seven regressing keratoacanthomas tended to show flattening before a decrease in diameter. Histopathologically, there was variable epidermal hyperplasia with generally prominent hyperkeratosis, retained crateriform architecture, and dermal fibrosis. Limitations: This study has a small sample size. Conclusions: Regressing keratoacanthomas show persistent crateriform architecture, clinically and histopathologically. Lesions become flatter before decreasing in diameter, and keratinocytes appear banal and lack glassy pink cytoplasm during regression. (J Am Acad Dermatol 2012;67:1008-12.)