Of note are the estrogen receptor-positive (ER+) breast cancer phase II trials (NCT04190056, NCT00828854, NCT00676663) testing efficacy of epidrugs in combination with traditional therapies, reflective of recent advancements in our understanding of the epigenetic mechanisms governing ER+ breast cancer growth, metastasis, and treatment resistance. This evidence concerns the gene ESR1 and breast carcinoma.