To identify potential regulators of HER2 shedding in trastuzumab resistance, peripheral blood samples and breast cancer biopsies were collected from 61 patients with locally advanced or early stage HER2+ breast cancer (with “early stage” defined as lymph node–positive or tumor size over 5 cm in diameter) before they received neoadjuvant trastuzumab therapy. This evidence concerns the gene ERBB2 and breast carcinoma.