Cytochrome P450 (CYP) enzymes perform a major role in the metabolic activation of polycyclic aromatic hydrocarbons (PAHs) to epoxide intermediates, suggesting a link between PAHs, the CYP pathway, and cancer development that cytochrome P450 1A1 (CYP1A1) is believed to be the most important enzyme in this link16 and CYP1A1, as a drug-metabolizing enzyme, is among the main enzymes imported in the processing of tobacco-related carcinogens17. The gene discussed is CYP1A1; the disease is cancer.