Epigenomic, transcriptomic or genomic analysis of Luminal type primary breast tumours which metastasize have proposed loss of ESR1 (ER) gene expression due to either ESR1 (ER) hypermethylation [18], basal-like molecular features such as TP53 and/or PIK3CA mutations [16] or increased expression of FGFR4 [46] and activation of corresponding growth factor signalling pathways may be associated with Luminal A/B to HER2-enriched subtype switching. The gene discussed is ESR1; the disease is breast neoplasm.