ALTERED P53 IN MICRODISSECTED, METACHRONOUS, PREMALIGNANT AND MALIGNANT ORAL LESIONS HOM THE SAME PATIENTS

Aims-To determine whether mutant p53 alleles harboured by malignant tu mours of the oral cavity were also present in previous premalignant le sions at the same site. Methods-Paraffin embedded tumour specimens alo ng with their premalignant counterparts were analysed for p53 alterati ons using immunohistochemistry, microdissection, polymerase chain reac tion amplification, and DNA sequencing. Results-Malignant lesions from five of eight patients showed overexpression of p53 protein by immuno histochemistry. Upon DNA sequencing, two of these five specimens had p 53 mutations. Of the five patients whose cancers showed p53 overexpres sion by immunohistochemistry, three had previous premalignant lesions that also had immunohistochemically detectable p53 protein. However, D NA sequencing showed that none of these three had mutations in the p53 gene. The remaining five premalignant lesions had no immunohistochemi cally detectable p53 protein. Conclusions-Some premalignant lesions ha ve increased p53 protein which can be detected by staining with antibo dy to p53. This staining is not caused by mutations in p53 that are fo und in subsequent tumours at the same site.