The triple negative/basal-like (TN/BL) breast cancer subtype comprises ∼15% of all breast cancers and is defined as estrogen (ERα)-, progesterone (PR)- and HER2- (not amplified) receptor negativity, but basal-associated markers- (e.g., cytokeratin 5/6 and 17) positivity [19]. This evidence concerns the gene ESR1 and breast cancer.