p53 mutations and chromosome instability in basal cell carcinomas developed at an early or late age

Tumor DNA from 45 primary basal cell carcinoma (BCC) biopsies was screened for p53 gene mutations, chromosome 9 allele loss, and microsatellite instability. p53 mutation frequency increased significantly as a function of the age at BCC onset ranging from 6% (1/16) in early BCC (before age 40 years) to 35% (10/29) in late BCC. All p53 mutations found implicated sunlight as the mutagen. Chromosome 9 instability (allele loss or microsatellite instability) was detected at high frequency (38%) independently of age at tumor onset. Allelic loss was confined to chromosome 9q, whereas microsatellite instability was observed prevalently on chromosome 9p often in association with a replication error (RER+) phenotype. Most of our late BCC patients reported occupational sun exposure, while early BCC patients recalled childhood (0-20 years) recreational sun exposure. These data suggest that chronic exposure to sunlight is responsible for accumulation of p53 mutations and thus for late BCC appearance, whereas acute UV exposure in childhood and adolescence leads to early skin cancer development in genetically susceptible individuals via a p53-independent pathway.