To investigate the role of CXCR4 in trastuzumab resistance in breast cancer patients, using RPPA, we analyzed CXCR4 expression in fresh-frozen tumor tissues from 112 untreated patients (primary breast tumor tissues) and 72 patients who received neoadjuvant therapy before surgery (residual tumor tissues) that we had collected and some of which were used in our previous studies [41], among them, several patients with HER2 + breast cancer received Herceptin and Taxol (paclitaxel), or Taxotere (docetaxel). Here, ERBB2 is linked to breast cancer.