We reported a patient with actinic keratosis and keratoachantoma. Both tumors were on her dorsum pedis. Since those area were notably close, to investigate the cause of diseases, immunohistochemical staining and TdT-mediated dUTP-biotin nick end labeling (TUNEL) method were performed on theses skin samples. P53 immunoreactivity was not observed in the keratoacanthoma, and positive staining was seen in the actinic keratosis. In contrast, apoptosis was not detected on the actinic keratosis and

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... well detected on the central and peripheral portion of keratoacanthoma. This suggests P53 immunoreactivity and detection of apoptosis are very beneficial methods for differentiation of diagnosis of keratoacanthoma and squamous cell carcinoma.