In addition to the traditional classifications using these biomarkers, in recent years, whole genome DNA microarrays have been utilised to further classify this disease, initially into five molecular subtypes based on gene expression profiles, namely luminal A and luminal B (ER-positive tumours), HER2 (HER2-positive tumours), basal and normal-like tumours [5,6] and subsequently into at least ten further molecular subtypes using both copy number and gene expression data [7]. This evidence concerns the gene ESR1 and neoplasm.