To determine whether the quercetin-induced suppression of COX-2 expression is mediated by inhibition of the binding of the functionally important transactivators to COX-2 promoter in human breast cancer cells, we tested the effect of quercetin on the binding activities of CREB-2, C-Fos, C/EBPβ, NF-κB p65, and NF-κB p50 to the COX-2 promoter in MDA-MB-231 cells. This evidence concerns the gene NFKB1 and breast cancer.