Long-term outcomes of neoadjuvant treatment of HER2-positive breast cancer

Long-term outcomes for women with a diagnosis of human epidermal growth factor receptor 2 (HER2)-driven early-stage breast cancer have significantly improved since the advent of HER2-targeted therapy. Although the first studies in the early-stage setting focused on the adjuvant use of trastuzumab plus chemotherapy, clinical trials increasingly are using a neoadjuvant design to evaluate novel HER2-targeted therapies. Neoadjuvant therapy downstages locally advanced breast cancer, improves rates of breast conservation, and provides information regarding the responsiveness of a cancer to systemic therapy; in addition, studies have shown that the pathologic response to neoadjuvant therapy is correlated with event-free and overall survival. Given these advantages, multiple studies of neoadjuvant therapy, several of which have reported longer-term outcomes, have been conducted to evaluate HER2-targeted therapies. This review summarizes available data from prior and ongoing neoadjuvant trials in HER2-positive breast cancer, focusing on those studies that have reported not only pathologic response rates but also event-free, disease-free, and/or overall survival. The long-term outcomes associated with the achievement of a pathologic complete response are explored, and the comparisons of pathologic complete response rates, event-free survival, and overall survival reported for different HER2-targeted regimens are reviewed.