ERBB2 and breast carcinoma: TAM is the oldest and most prescribed selective estrogen receptor modulator (SERM) as, overall, 75% of breast cancer patients are estrogen receptor (ER)-positive [5,6,7], while the remaining 25% are ER-negative and either exhibit overexpression of human epidermal growth factor receptor 2 (HER2) or are triple-negative breast cancers.