CDKN1B and breast carcinoma: In fact, in one of the human breast cancer cells (AU565), both 4-hydroxytamoxifen and tamoxifen were observed to up-regulate the activity of -1797 p27 (p27-Kpn I), suggesting that the global transcriptional rate could be lower in these cells compared to other human breast cancer cells (MDA-MB-231 and MCF7).