ERBB2 and ductal breast carcinoma in situ: Previous clinical studies identified HER2 (also know as neu) overexpression in DCIS lesions as a predictive indicator for the transition of in situ to invasive breast cancer.3 However, while HER2 overexpression is seen in up to 50% of all DCIS lesions, <25% of invasive breast carcinomas overexpress HER2,4 suggesting that HER2 alone is not sufficient for full malignant transformation.