p53 gene mutations in squamous cell carcinoma occurring in scars: comparison with p53 protein immunoreactivity.

We determined the relationship between p53 expression and p53 gene mutations in squamous cell carcinoma occurring in scars and unrelated to UV light irradiation. We analyzed biopsy specimens obtained from three patients with squamous cell carcinoma. A monoclonal antibody against p53 (DO-7) was used for the immunohistochemical analysis. p53 gene mutations were detected by the polymerase chain reaction and single-strand conformation polymorphism analysis and direct DNA sequencing. p53 overexpression was observed in atypical squamous cells of one case. Those of two other cases, however, showed negative immunoreactivity to p53. Exon 6 of the p53 gene in all three cases and exon 7 in one case showed electrophoretic mobility shifts in polymerase chain reaction and single-strand conformation polymorphism analysis. DNA sequencing analysis showed a missense mutation and a silent mutation in exon 6 of the case with p53 overexpression, a three-base deletion in exon 6 of one case with no p53 overexpression, and a three-base deletion in exon 6 and a missense mutation in exon 7 of another such case. Although immunohistochemical overexpression of p53 has been thought to result from p53 gene mutations, our results suggest that negative immunoreactivity to p53 also can result from p53 gene mutations, for example, short gene deletions.