ERBB2 and breast cancer: The lifetime risk of developing breast cancer is approximately 1 in 8 for women, with over 40% of cases occurring in those aged 65 and older, who contribute to nearly 60% of breast cancer-related mortality.4 For women under 49, the risk is 1 in 53, rising to 1 in 43 for those aged 50–59, 1 in 23 for those aged 60–69, and peaking at 1 in 15 for women over 70.4 The human epidermal growth factor receptor 2 (HER2/neu), encoded by the ERBB2 gene on chromosome 17q, is a transmembrane receptor tyrosine kinase that regulates cell growth, division, and repair under normal physiological conditions.5