Intertumoral heterogeneity within breast cancer patients, for example, exhibiting different molecular subtypes based on immunohistochemical markers like Estrogen Receptor (ER) or Her2, has been the basis of successful targeted therapeutic approaches (Turashvili and Brogi, 2017; Januskeviciene and Petrikaite, 2019). This evidence concerns the gene ESR1 and breast carcinoma.