TP53 mutation spectra and load: a tool for generating hypotheses on the etiology of cancer.

Among genetic alterations, the activation of proto-oncogenes and inactivation of tumour suppressor genes in affected cells are considered to be the core molecular events that provide a selective growth advantage and clonal expansion during the multistep process of carcinogenesis. The TP53 tumour suppressor gene is mutated in about half of all human cancer cases. The p53 protein modulates multiple cellular functions, such as gene transcription, DNA synthesis and repair, cell cycle arrest, senescence and apoptosis. Mutations in the TP53 gene can abrogate these functions, leading to genetic instability and progression to cancer. The molecular archaeology of the TP53 mutation spectrum generates hypotheses concerning the etiology and molecular pathogenesis of each type of cancer. The spectrum of somatic mutations in the TP53 gene, of which 75% are missense mutations, implicates environmental carcinogens and endogenous processes in the etiology of human cancer. The presence of a characteristic TP53 mutation can also manifest a molecular link between exposure to a particular carcinogen and a specific type of human cancer, e.g. exposure to aflatoxin B1 (AFB1) and codon 249 mutations in hepatocellular carcinoma; exposure to ultraviolet (UV) light and C:C-->T:T tandem mutations in skin cancer; and cigarette smoking and the prevalence of G-->T transversions in lung cancer. Although exogenous carcinogens have been shown to target p53 selectively, evidence supporting the endogenous insult of TP53 from oxyradicals and nitrogen-oxyradicals is also accumulating. TP53 mutations can be a biomarker of carcinogen effect. Determining the characteristic TP53 mutation load in non-tumorous tissue, using a highly sensitive mutation assay, can indicate exposure to a specific carcinogen and may also help in identifying individuals at an increased risk of cancer.