Sequencing of the tumor DNA as well as further mechanistic studies provided evidence that PAHs initiate carcinogenesis by inducing mutations primarily in the Ha-Ras oncogene and that this process requires a metabolic conversion of the per se non-toxic chemicals to highly reactive metabolites, a process which is primarily carried out by AHR-regulated cytochrome P450 (CYP) monooxygenases (10–12). Here, AHR is linked to neoplasm.