Although therapeutic efforts so far have focused more on triple negative breast cancer (TNBC), ERβ expression in tissue microarrays of breast cancer was significantly associated with expression of ERα and progesterone receptor and, when analyzed by molecular classification, higher in luminal A (72%) and luminal B (68%) breast cancers as compared to HER2+ and basal like sub-types (55 and 60%) (131). This evidence concerns the gene ESR1 and breast cancer.