ERBB2 and breast cancer: For the past 2 decades, a binary algorithm has been used that classifies breast cancer into HER2 positive (immunohistochemistry (IHC) scores 3+ and/or 2+ in situ hybridisation (ISH) amplified) and HER2 negative (IHC scores 0,1 or 2+ ISH non amplified) [2,3].