ESR1 and breast cancer: Consequently, we took advantage of the «trial quality» collection of well annotated formalin-fixed paraffin-embedded (FFPE) tumor blocks from early breast cancer patients randomized in two prospective clinical trials of the Hellenic Cooperative Oncology Group (HeCOG) in order to globally profile ESR1 gene copy number aberrations, mRNA and protein expression and study their incidence, correlations, prognostic and predictive utility [12], [13].