ESR1 and neoplasm: For example, co-culture of premalignant mammary cells (EIII8, a subclone of MCF10A) or invasive IDC cells (MCF7) with fibroblasts derived from ER/PR-positive tumours enhanced inhibitory effect of tamoxifen on cell growth in 3D cultures, whereas fibroblasts from of ER/PR-negative tumours triggered an opposite effect i.e. promoted acquisition of resistance to tamoxifen [35].