Man-made carcinogens, natural genotoxic agents in the environment, as well as ionizing and ultraviolet radiation can damage DNA and are a constant threat to genome integrity. Throughout the evolution oflife, complex DNA repair systems have developed in all living organisms to cope with this damage. Unrepaired DNA lesions can promote genetic alterations (mutations) that may be linked to an altered phenotype, and, if growth-controlling genes are involved, these mutations can lead to cell transformation and the development of malignant tumors. Proto- oncogenes and tumor suppressor genes may be...