However, BRD7 was found to function as a tumor suppressor in breast cancer whether in ER-positive breast cancer MCF-7 cells or ER-negative MDA-MB-231 and MDA-MB-453 cells, supporting that BRD7 function as tumor suppressor independent of ER but other mechanism, including the regulation of BRD7 on HIF1α. This evidence concerns the gene ESR1 and breast cancer.