Systemic therapy for HER2-positive early-stage breast cancer

The advent of the targeted monoclonal antbody trastuzumab for treatment of human epidermal growth factor receptor 2 (HER2)-positive breast cancer marked a revolution in the understanding and management of mammary carcinoma and, in practice, separated this subtype from other kinds of primary breast malignancy. Long term follow-up from the initial large adjuvant trials continue to show remarkably positive results. Currently, at least four additional agents targeting this receptor, using different and complementary mechanisms of action compared with trastuzumab, have been incorporated into clinical trials. The small molecule tyrosine kinase inhibitors lapatinib and neratinib, in addition to the antibody pertuzumab and the antibody-drug conjugate trastuzumab-ematansine, have shown efficacy in metastatic breast cancer and are being evaluated both in neoadjuvant and adjuvant trials for early stage disease. The cytotoxic chemotherapy regimens used in combination with these agents also are evolving and different therapeutic approaches are emerging for patients depending on their relative level of risk from their cancers, thus moving clinical management toward individualized therapy. Much has been learned about managing the toxicities of treatment and pre-operative approaches have provided a means of assessing the sensitivity of individual patients' cancers to specific treatment regimens. This review traces the development of these studies and focuses on improvements in adjuvant and neoadjuvant therapy for patients with HER2-positive disease whose prognosis has changed in the last decade from dire to favorable. A path forward has been set by which the goal of cure is attainable for almost all patients faced with this aggressive form of breast cancer.