Some ER‐positive/HER2‐positive tumours behave more like the luminal A sub‐type (i.e., ER‐driven cancer) and others as HER2‐E tumours (HER2‐driven cancer) or a combination of both, which requires a multi‐pronged targeted blockade of both ER and HER2 pathways [42]. This evidence concerns the gene ESR1 and neoplasm.