Importantly, each of these small molecules were named as ER coregulator binding modulators (ERXs, where X refers to their multiple potential and unknown targets) had differential activities in ER-positive breast cancer cells (Figure 1A, Figure 1—figure supplement 1C), confirming our hypothesis that the sequences flanking the core LXXLL motif could determine specificity and activity. This evidence concerns the gene ESR1 and breast cancer.