A common example of this is the interaction of certain SSRIs (including fluoxetine and paroxetine, which are concurrently prescribed in 20–30% of breast cancer patients) with tamoxifen, which reduces the metabolism of tamoxifen to its active metabolite, endoxifen, by inhibiting the hepatic CYP2D6 enzyme. This evidence concerns the gene CYP2D6 and breast cancer.