Raised risk in relation to obesity has been reported in several studies1, 2, 3, 4, 5, 6, 7, 8, 9 (Swerdlow et al, in press), and we have shown that this applies to both invasive and in situ tumours and is stronger for human epidermal growth factor receptor 2 (HER‐2) positive than HER‐2 negative tumours (Swerdlow et al, in press), for reasons unknown. The gene discussed is ERBB2; the disease is obesity disorder.