CYP3A4 and lung cancer: Although the mechanism by which β-carotene increases the incidence of lung cancer remains to be elucidated, it has been speculated that the expression of the cytochrome P450 (CYP) enzymes, including CYP1A1/2 and CYP3A, that is induced by β-carotene may be responsible for the activation of pro-carcinogens and thus, the increase in the risk of lung cancer (2).