ERBB2 and cancer: The Med1 gene is located within the 17q12 region of chromosome 17, also known as the HER2 amplicon, which is amplified in approximately 20%–25% of breast tumors and binds directly to the ER through the LXXLL motif.32 This suggests that Med1 is a key regulator of cellular processes involved in breast tumor growth, metastasis, cancer stem cell formation, and treatment resistance.