DE-ESCALATING TREATMENT FOR HER2-POSITIVE EARLY BREAST CANCER.

HER2-positive breast cancers are defined by amplification of the cerbB2 gene and overexpression of its protein HER2. This subtype of breast cancer is aggressive, grows rapidly, and metastasizes early. However, new treatments targeting HER2 combined with chemotherapy have dramatically altered the course of patients harboring this type of breast cancer. Traditionally, these patients have been treated with aggressive combination chemotherapy, combined with trastuzumab, an antibody that blocks HER2 signaling and also induces antibody-dependent cellular cytotoxicity. Trastuzumab combined with newer drugs that also block HER2 signaling has been shown to be effective even in the absence of chemotherapy. Significant pathologic complete response (pCR) rates have been observed with dual targeted therapy in preclinical studies and in neoadjuvant trials in patients without chemotherapy. Before this de-escalation strategy can become part of routine clinical care, biomarkers need to be developed that identify patients who either do or do not respond well to such therapies.