Our multivariable analyses controlled for two major potential confounders, ER status and breast surgery, but we were unable to adjust for other risk factors for recurrence such as HER2 status and trastuzumab therapy as HER2 was not routinely reported to cancer networks in Scotland at the time of this study, and trastuzumab was being introduced as routine therapy on NHS Scotland around the same time. The gene discussed is ERBB2; the disease is cancer.