Escalating and De-escalating Therapy for Early-Stage HER2-Positive Breast Cancer.

Untreated, HER2+ disease is the most aggressive breast cancer phenotype; however, the development of multiple highly effective HER2-targeting drugs has transformed treatment and survival. These drugs include the anti-HER2 monoclonal antibodies trastuzumab and pertuzumab; small molecule inhibitors lapatinib, neratinib, and tucatinib; and antibody-drug conjugates trastuzumab emtansine (T-DM1) and now trastuzumab deroxtecan. More complex regimens using these drugs continue to improve outcomes, but the incremental benefits of these advances are often modest. Improved outcomes came from the addition of HER2-targeted therapies to conventional chemotherapy, beginning with trastuzumab, then pertuzumab added to trastuzumab, or with neratinib given for the year after trastuzumab. Neoadjuvant, or preoperative, administration of chemotherapy plus HER2-targeting allows surgical deescalation and tailoring treatment by pathologic complete response (pCR) to therapy. Patients with pCR after conventional therapy have excellent outcomes; what we now know is that the poorer outcomes associated with residual disease can be ameliorated with adjuvant T-DM1. However, as we have developed more complex, effective, and expensive therapy to maximize outcomes, it is also true that we are overtreating many patients. In stage I HER2+ breast cancer, there are excellent outcomes with paclitaxel plus trastuzumab or T-DM1 alone. Higher clinical stage HER2+ disease is still treated aggressively, although intrinsic subtype or activated immune tumor microenvironment may identify those with augmented treatment response or better outcome. It is likely that future strategies to escalate and de-escalate treatment with less chemotherapy, fewer anti-HER2 drugs, or shorter duration will depend upon integrated clinical and genomic modeling.