The group with HER2-enriched tumours had the highest proportion of breast cancer deaths (34.1%) over the follow-up period (median follow-up [IQR] = 4.59 years [2.77, 7.28]) and the group with luminal A tumours had the lowest proportion of breast cancer deaths during this period (8.3%) (Table 1). Here, ERBB2 is linked to breast cancer.