p53 gene mutations in sequential oral epithelial dysplasias and squamous cell carcinomas

Previous studies of oral cancer have suggested that alterations of the p53 tumour suppressor gene occur early in the precancerous stage of development. However, these observations have been based on cross-sectional assessment of abnormal p53 protein staining by immunohistochemistry and may not necessarily reflect gene changes. The purpose of this longitudinal study was to examine the changes in the p53 gene in progressive, sequential epithelial dysplasias and carcinomas from the oral cavity. The study analysed 24 formalin-fixed, paraffin-embedded tissue biopsies from ten patients with two or more temporally distinct lesions from the same site in the oral cavity with the diagnosis of hyperkeratosis, epithelial dysplasia, carcinoma in situ or squamous cell carcinoma. Exons 5-8 of the p53 gene were amplified from genomic DNA using intronic primers and directly sequenced using fluorescent-labelled primers. Standard immunohistochemistry with the DO7 monoclonal antibody was used to detect mutant and wild-type p53 protein. Mutations of the p53 gene were identified in 9 of 24 samples. Eight were missense mutations and one occurred at a splice site. In six patients, mutations of the p53 gene occurred late after the transformation of epithelial dysplasia to carcinoma. In two patients with progressive dysplasia, but who had yet to develop invasive carcinoma, p53 missense mutations occurred at the carcinoma in situ stage in one case and in a moderate dysplasia in the other. There was an inconsistent relationship between gene mutations and the level of p53 protein staining by immunohistochemistry. It is concluded that during oral carcinogenesis, p53 gene mutations seem to occur relatively late and are associated with transformation to the invasive phenotype.