ESR1 and breast cancer: Discs large homolog 5 (DLG5) is a member of the membrane‐associated guanylate kinase (MAGUK) family, and a necessary component for the formation and maintenance of epithelial tube and cell polarity.9 A recent study has showed that DLG5 can inhibit the progression of ER+ breast cancers and DLG5 deficiency promotes the migration and proliferation of ER+ breast cancer cells.10 DLG5 expression is upregulated in Luminal type of breast cancer tissues and positively correlated with ER expression.