ERBB2 and breast cancer: There are 4 major types: Endocrine receptor (estrogen or progesterone receptor) positive, human epidermal growth factor receptor 2 (HER2) positive, triple positive (estrogen, progesterone and HER2 receptor positive) and triple negative (absence of estrogen, progesterone and HER2 receptors) (http://www.cancer.org/cancer/breastcancer/detailedguide/breast-cancer-classifying)5.