Nonetheless, resistance to tamoxifen poses a substantial obstacle in breast cancer treatment.[35] Micro-RNA (MiR)-873 is often downregulated in breast cancer, and the overexpression of MiR-873 in ER-positive breast cancer can lead to a weakening of the transcriptional activity of ERα via the regulation of ERα phosphorylation. The gene discussed is ESR1; the disease is breast carcinoma.