Phase II clinical trials evaluating the efficacy of these DNMT inhibitors in combined therapy, such as NCT03295552 (decitabine plus carboplatin for metastatic TNBC), NCT02957968 (decitabine plus pembrolizumab for advanced HER2− BC), and NCT02811497 (azacitidine plus durvalumab for ER+/HER2− BC) trials, are still ongoing and/or did not report any available results. This evidence concerns the gene ESR1 and breast cancer.