In our study, the DFS and OS hazard ratios for severe obesity (reference group underweight/normal weight) were similar for the luminal B-like, HER2-positive and triple-negative subtypes (range 2.78–3.85), indicating that the lack of significance in the luminal B-like and HER2- positive subgroups found in our study might be attributable to the smaller number of severely obese patients and the resulting reduced statistical power. The gene discussed is ERBB2; the disease is obesity disorder.