p53 expression in pseudoepitheliomatous hyperplasia, keratoacanthoma, and squamous cell carcinoma of skin.

BACKGROUND: Expression of p53 protein has been described in a variety of human malignant tumors. Recent reports have also demonstrated its presence in benign and reactive lesions. The significance of p53 expression is unclear.
METHODS: This study examines the p53 expression in proliferative lesions of skin, including 6 pseudoepitheliomatous hyperplasia, 33 keratoacanthoma, and 45 squamous cell carcinoma, and to evaluate its significance.
RESULTS: p53 expression was observed in all of the six cases of pseudoepitheliomatous hyperplasia, 78.8% of keratoacanthoma, and 75.5% of squamous cell carcinoma. The staining pattern of pseudoepitheliomatous hyperplasia and keratoacanthoma was generally less intense and extensive compared with that of squamous cell carcinoma. A keratoacanthoma with nuclear atypia that showed strong and extensive p53 staining was also encountered. The perilesional skin in sun-exposed sites often showed the presence of p53-positive keratinocytes. Control skin taken from the buttock was negative for p53 protein. Conversely, p53 was often expressed in carcinomas arising from sun-exposed as well as sun-protected sites. p53 positivity involved mainly the undifferentiated cells at the base of the epidermis or periphery of tumor cords. Differentiated keratinized cells were not stained. p53-positive fibroblasts were also noted in the inflammatory and granulation tissues of pseudoepitheliomatous hyperplasia.
CONCLUSIONS: p53 expression in skin is common and appears to be an early event in a series of genetic alterations reflecting underlying actinic damage, which may lead to but does not necessarily indicate neoplastic or malignant transformation. Because p53 staining is seen in proliferative and undifferentiated cells and ceases to be expressed when the cells differentiate, it appears that the expression of p53 protein, mutant or wild-type, is an indicator of immaturity and proliferative capacity of the cell rather than one of neoplasia or malignancy.