ERBB2 and ductal breast carcinoma in situ: It is paradoxical in a way that HER2 is a powerful oncogene whose overexpression promotes the progression of the tumour and is linked with a poorer clinical outcome in the invasive breast cancer 8, 9, but here the DCIS with HER2 overexpression seems to have no advantage over those of HER2-negative to further develop into invasive breast cancer.