CYP1A1 and neoplasm: Yet, while CYP1A1 transcription is commonly induced through the aryl hydrocarbon receptor (AhR), MФ supernatants were not able to inhibit AhR agonist 2,3,7,8-tetrachlorodibenzodioxin (TCDD)-induced expression of CYP1A1 (S2 Fig), supporting an AhR-independent mode of transcriptional repression of CYP1A1 in tumor cells elicited by MФs.