ERBB2 and breast cancer: Given that few population-based cancer registries worldwide routinely collect data on Ki-67, epidermal growth factor receptor, and cytokeratin testing [6,7,12,14,15], the BC subtypes are generally categorized as hormone receptor positive (HR+), based on expression of oestrogen and/or progesterone receptor; HER2-positive (HER2+), regardless of hormone receptor status; and triple-negative, lacking expression of HER2 and oestrogen or progesterone receptors [6,7].