Because the impact on BMI and breast cancer outcomes was masked by the effect of the ER and/or PR+/HER2- and ER and PR-/HER2+ subgroups, a weaker association between BMI and poor outcomes may exist in patients in the ER and/or PR+/HER2+ and ER and PR-/HER2- subgroup. This evidence concerns the gene ERBB2 and breast cancer.