Compared with pure IDC, IDC-DCIS tumours were more often ER positive (81.5 vs 74.0%, P=0.002), PR positive (74.7 vs 70.5%, P=0.114), and/or HER2 positive (25.5 vs 16.2%, P<0.0005). The gene discussed is ERBB2; the disease is ductal breast carcinoma in situ.