P53 EXPRESSION IRE 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 p resence in benign and reactive lesions. The significance of p53 expres sion is unclear. Methods. This study examines the p53 expression in pr oliferative lesions of skin, including 6 pseudoepitheliomatous hyperpl asia, 33 keratoacanthoma, and 45 squamous cell carcinoma, and to evalu ate its significance. Results. p53 expression was observed in all of t he six cases of pseudoepitheliomatous hyperplasia, 78.8% of keratoacan thoma, and 75.5% of squamous cell carcinoma. The staining pattern of p seudoepitheliomatous hyperplasia and keratoacanthoma was generally les s intense and extensive compared with that of squamous cell carcinoma. A keratoacanthoma. with nuclear atypia that showed strong and extensi ve p53 staining was also encountered. The perilesional skin in sun-exp osed sites often showed the presence of p53-positive keratinocytes. Co ntrol skin taken from the buttock was negative for p53 protein. Conver sely, p53 was often expressed in carcinomas arising from sun-exposed a s well as sun-protected sites, p53 positivity involved mainly the undi fferentiated 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 tissu es of pseudoepitheliomatous hyperplasia. Conclusions. p53 expression i n skin is common and appears to be an early event in a series of genet ic alterations reflecting underlying actinic damage, which may lead to but does not necessarily indicate neoplastic or malignant transformat ion. Because p53 staining is seen in proliferative and undifferentiate d cells and ceases to be expressed when the cells differentiate, it ap pears that the expression of p53 protein, mutant or wild-type, is an i ndicator of immaturity and proliferative capacity of the cell rather t han one of neoplasia or malignancy.