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.