Understanding the metabolite changes during cancer progression is relevant for diagnosis, follow-up and treatment, hence, this study addresses three mammary invasive ductal adenocarcinoma tumour lines that express similar levels of ER and PR but respond differently to ET (21), with the aim of characterising the metabolic profiles of neoplastic tissue compared to normal tissue (MG), and disclosing metabolic signatures discriminative of HD, HI and HIR tumors. The gene discussed is ESR1; the disease is cancer.