ERBB2 and breast cancer: HER2-positivity is a predictive factor of trastuzumab response, but although five out of six randomised phase III trials reported marked benefit of adjuvant trastuzumab for disease-free and overall survival (with reduction of recurrence and mortality by 20-40%) [34-38], there are no data on trastuzumab in pT1a-pT1b HER2-positive breast cancer.