Linear regression was adjusted for tumour size, histology, ER status, PR status, HER2 status, TN status and grade in the FOCUS study and the Nottingham Breast Cancer series (B 0.031, 95% CI 0.006–0.057, p = 0.016 and B 0.034, 95% CI 0.015–0.054, p < 0.001, respectively). This evidence concerns the gene ERBB2 and breast cancer.