AHR and cancer: Interestingly, while AhR and AhRR—the markers that were possibly related to carcinogenesis—were not found to be expressed in the cancer cells of the tumor samples, the expression of CYP1A1 as the main marker of AhR activation [46] was observed in some cancer cells obtained from tumor samples sq1 and ad7 of both smoking and non-smoking patients, respectively (Table 2, Figure S2).