Figure 8.

Keratoacanthoma, hyperkeratotic squamous papilloma, and in situ squamous cell carcinoma (Bowen disease). (A). Keratoacanthoma. Tegument covered by a keratinized stratified squamous epithelium, composed of squamous cells with minimal atypia, exhibiting pronounced orthokeratotic hyperkeratosis phenomena. (B). Hyperkeratotic squamous papilloma. Keratinized stratified squamous epithelium, without atypia, presenting a papillomatous formation on the surface covered by a keratinized stratified squamous epithelium with marked orthokeratotic hyperkeratosis, along with an acanthotic spinous layer. (C). In situ squamous cell carcinoma (Bowen disease). Skin fragment covered by intact keratinized stratified squamous epithelium, exhibiting marked dysplasia throughout its thickness. Tumor cells display pleomorphism, enlarged nuclei, and irregular nuclear membranes, with numerous mitoses. The tumor cells do not infiltrate the underlying dermis.