ERBB2 and breast cancer: The molecular subtypes used in this study are based on the recommended definition by the 13th St Gallen International Breast Cancer Conference (2013) Expert Panel review, defining Luminal A as (ER and PR positive, HER2 negative, Ki-67 low), Luminal B (HER2 negative) (ER-positive, HER negative and at least one of Ki-67 high or PR negative), Luminal B (HER2 positive) (ER-positive, HER2 positive and any of Ki-67 high or PR positive), HER2-enriched (HER2 positive, ER-negative, PR negative) and Triple Negative Breast Cancer (TNBC) (ER-negative, PR negative, HER2 negative).