ERBB2 and breast cancer: A US population-based study showed the most common breast cancer subtype is hormone receptor (HR)-positive (+), human epidermal growth factor receptor 2 (HER2)-negative (-), occurring in 73% of all patients, followed by triple negative (HR-, HER2- [TNBC]; 12%), HR+, HER2+ (10%), and HR-, HER2+ (5%) [2].