AHR and Cowden syndrome 1: Although the AhR may mediate carcinogenicity induced by individual components of CS, such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) [18] and benzo[a]pyrene [19], it simultaneously protects against many of the pathogenic effects of CS in the lung [9,10,11,12,20].