Expression of mismatch repair enzymes, hMLH1 and hMSH2 is not associated with microsatellite instability and P53 protein accumulation in basal cell carcinoma
Ultraviolet (UV) radiation plays a pivotal role in skin damage and photocarcinogenesis. The basic mechanism of phototoxicity lies in DNA damage, and involves mutation of tumor suppressor genes, oncogenes and genes directly involved in the control of the stability of genome, such as the mismatch repair (MR) genes. The goal of this study was to evaluate the role of p53 and hMSH2 in the UV-related carcinogenetic process. An immunohistochemical study for p53 and hMSH2 was performed in a series of 43 basal cell carcinomas (BCC) and 60 melanomas (MM) from photoexposed areas of head and neck region, comparing the findings with follow-up. A deregulated p53 expression characterized less differentiated, more aggressive BCC (BCC2) but not the well-differentiated ones (BCC1). The hMSH2 protein was present, though expressed at varying levels, in 18 out of 21 BCC1 cases and in 4 out of 22 BCC2. In the remaining 3 cases of BCC1 and 18 cases of BCC2, a complete absence of hMSH2 expression was found, correlating directly with the presence of recurrence and/or death of the disease in case of melanoma (p<0.05). Overall, the expression of hMSH2 correlated inversely with the p53 overexpression (p<0.01). In MM, p53 was found overexpressed in 81.6% of the cases, and this correlated positively with the level of infiltration and with the presence of relapses (p<0.01) or metastasis (p<0.01) and inversely with the disease-free interval (p<0.05). These results are in agreement with the reported association between p53 deregulation and a more aggressive cancer phenotype. The evaluation of the expression of p53 and hMSH2 could improve the management of patients with BCC and MM, and could have a role also in the evaluation of the early cutaneous photo-inducted damage, contributing to the identification of presymptomatic patients predisposed to the development of UV-related new skin tumors, who could become candidates for chemoprevention trials.