ERBB2 and breast cancer: ,2 The proportional risk reduction is the same across subgroups defined by tumour size, oestrogen receptor (ER) expression, human epidermal growth factor receptor 2 (HER2) expression, histological type, grade, Ki67, age and nodal status according to a meta-analysis of individual patient data conducted by the Early Breast Cancer Trialists’ Collaborative Group (EBCTCG), although most patients in these analyses were node-positive.1