Neoadjuvant therapy has become a standard clinical practice to downsize the tumor and increase the breast-conserving rate. The addition of trastuzumab to neoadjuvant chemotherapy roughly doubles the proportion of patients with HER2-positive breast cancer who achieve pathological complete response (pCR). Patients with pCR show better prognosis compared with those with residual disease after neoadjuvant therapy. Targeting the HER2 pathway with trastuzumab and pertuzumab can further increase the pCR rate. Several studies have shown that neoadjuvant chemotherapy with trastuzumab plus pertuzumab is tolerable, increases the pCR rate compared with trastuzumab alone, and results in about 50-70% pCR rate. One of the most important studies on neoadjuvant therapy is the KATHERINE trial, in which improved prognostic outcome for patients with residual disease after neoadjuvant therapy was observed. In the trial, improved invasive disease-free survival (DFS) was observed with the administration of postoperative trastuzumab emtansine in patients with HER2-positive breast cancer who had residual disease after neoadjuvant therapy. The indication of neoadjuvant therapy in patients with HER2-positive breast cancer may be changed because the opportunity for residual disease-guided approach, demonstrated in the KATHERINE trial, will be lost when patients had first undergone surgery. Translational studies are promising for further patient selection for HER2-targeted therapy and the development of a novel treatment strategy including PI3K-targeted therapy and immune checkpoint inhibitors. Feasibility studies to evaluate the ability of needle-biopsy to predict pCR after neoadjuvant therapy suggested that standardization and refinements in biopsy procedure (i.e., needle size, number of samples, etc.) are essential for the design of clinical trials of omitted surgery for patients with radiologic complete response.
Keywords: Breast neoplasms; ErbB-2; neoadjuvant therapies; pertuzumab; trastuzumab.