DETECTION OF THE P53 GENE DELETION BY DUAL-COLOR FLUORESCENCE IN-SITUHYBRIDIZATION IN SQUAMOUS-CELL CARCINOMA OF THE SKIN

Dual color fluorescence in situ hybridization (FISH) analysis was appl ied to 22 squamous cell carcinomas (SCC) of the skin in order to detec t deletion of the p53 tumor suppressor gene in interphase nuclei using a cosmid probe for p53 and a centromeric probe for chromosome 17. Few er p53 signals than 17 centromeric signals and zero or one cosmid sign als were observed in 5.6+/-4.9% (mean +/- SD) of controls. Based on th is, 20% deletion was established as the cutoff line to define deletion of the p53 gene. Twenty of the 22 SCC cases demonstrated p53 gene del etion according to this criterion. The percentage of cells with deleti on ranged from 22% to 59% (33.9+/-10.9%). The ratio between the copy n umber of chromosome 17 centromeres and p53 in the predominant populati on of the tumor nuclei with p53 gene deletion was either 2/1 or 1/1. M oreover, the major subfraction was composed of chromosome 17 disomic c ells 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 aneu somic cells is the main mechanism of p53 gene deletion in SCC of the s kin. Immunohistochemical p53 expression was frequently associated with the p53 gene deletion detected by FISH.