Abstract
Dual color fluorescence in situ hybridization (FISH) analysis was applied to 22 squamous cell carcinomas (SCC) of the skin in order to detect deletion of the p53 tumor suppressor gene in interphase nuclei using a cosmid probe for p53 and a centromeric probe for chromosome 17. Fewer p53 signals than 17 centromeric signals and zero or one cosmid signals were observed in 5.6±4.9% (mean±SD) of controls. Based on this, 20% deletion was established as the cutoff line to define deletion of the p53 gene. Twenty of the 22 SCC cases demonstrated p53 gene deletion according to this criterion. The percentage of cells with deletion ranged from 22% to 59% (33.9±10.9%). The ratio between the copy number of chromosome 17 centromeres and p53 in the predominant population of the tumor nuclei with p53 gene deletion was either 2/1 or 1/1. Moreover, the major subfraction was composed of chromosome 17 disomic cells in all cases. This suggests that either p53 gene deletion of one allele in disomic cells or the loss of an entire chromosome 17 in aneusomic cells is the main mechanism of p53 gene deletion in SCC of the skin. Immunohistochemical p53 expression was frequently associated with the p53 gene deletion detected by FISH.
