p53 protein expression and cell proliferation in non-neoplastic and neoplastic proliferative skin diseases

The p53 protein is essential for the regulation of cell proliferation and its aberrant accumulation is usually seen in malignant tumors but also occurs in squamous epithelium of inflammatory skin diseases characterized by hyperproliferation. The aim of this study is to elucidate the role of the p53 tumor suppressor protein in the pathogenesis of different hyperproliferative, non-malignant and malignant skin diseases, and to determine the association between p53 overexpression and cell proliferation. We also investigated the influence of aging on p53 and Ki-67 protein expression.

One hundred and fifty skin specimens divided into 30 samples each of normal skin (NS), psoriatic skin (PS), keratoacanthomas (KA), basal cell carcinomas (BCC), and squamous cell carcinomas (SCC) were examined immunohistochemically to assess p53 and Ki-67 protein expression.

p53 immunostaining of NS, PS, KA, BCC and SCC was detected in 39.0%, 46.7%, 66.7%, 80% and 86.7% of cases, respectively. Median values and ranges of p53 protein expression were as follows: 0.0% (range, 0.0-1.8%) in NS, 0.0% (range, 0.0-6.5%) in PS, 9.2% (range, 0.0-24.0%) in KA, 19.3% (range, 0.0-48.1%) in BCC and 30.1% (range, 0.0-68.1%) in SCC. p53- and Ki-67-positive cells were present in basal (NS) and suprabasal layers (PS), and not only in cancer nests of KA, BCC and SCC but also in dysplastic and even morphologically normal epidermis adjoining cancers. The positivity of p53 and Ki-67 proteins differed significantly among the groups, with no differences in p53 expression between NS and PS and in Ki-67 expression between PS and KA. Within all groups there was a significant correlation between p53 and Ki-67 expression. Lesion location and patient age, with the exception of location in PS and age in BCC, were significantly related to p53 and Ki-67 expression in all groups.

Our findings suggest that p53 overexpression occurs mainly in neoplastic skin lesions, although it may also occur in squamous epithelium of inflammatory skin diseases such as PS, as well as in normal skin epithelium. It is associated with cell proliferation in normal as well as altered epithelium. p53 protein overexpression is an age-related process and significantly associated with sun exposure, especially in NS and PS but also in KA and SCC. Our findings suggest that Ki-67 rate and p53 protein expression reflect the degree of malignancy in the examined cutaneous neoplasms.