CYP1A1 and neoplasm: In this regard, the authors demonstrated, through in vitro experiments on Ishikawa cell lines, that 6-PN and hop extract activate the ERa receptor and aryl hydrocarbon (AHR) signalling pathways, with 6-PN being able to increase tumour suppressor gene expression and the expression of genes involved in oestrogen metabolism, by upregulating the expression of cytochrome P450 1A1 (CYP1A1), which is involved in the oestrogen detoxification mechanism, to a greater extent.