A comprehensive meta-analysis integrating both clinicopathologic and gene expression data using different molecular BC subtypes demonstrated that proliferation is the underlying feature of most prognostic gene signatures and the most robust biomarker for predicting the clinical outcome in ER+/HER2−, however, the immune response and tumor invasion signals are the key molecular events impacting prognosis in ER−/HER2− and HER2+ molecular subtypes, respectively [36]. Here, ESR1 is linked to breast cancer.