Neoadjuvant single and dual HER2 blockade among patients with localized HER2-positive breast cancer.

Abstract

147 Background: Dual neoadjuvant HER2 directed therapy is offered only in a clinical trial setting and is not standard of care, but emerging data suggests targeting multiple mechanisms may be more effective. We conducted a comprehensive systematic review and meta-analysis to evaluate the impact of neoadjuvant dual and single agent HER2 blockade on breast conserving surgery (BCS), and on pathological complete response (pCR) for estrogen receptor (ER)+ and ER- tumors, as well as the impact of pCR on disease-free survival (DFS) and overall survival (OS) for HER2+ breast cancer. Methods: MEDLINE, EMBASE, and Cochrane Controlled Clinical Trials Register databases were queried to identify eligible trials. Inclusion criteria were prospective, neoadjuvant trials that had at least one arm with HER2 directed therapy, and reported pCR. Pooled relative risk ratios (RRs) and p values were estimated for endpoints using the random effects statistical model. Results: We identified 36 trials (N = 4130). High pCR rates (> 40%) were seen with anthracycline-based chemotherapy and trastuzumab alone, and non-anthracycline based dual HER2 blockade. The addition of trastuzumab to chemotherapy did not improve BCS rate (RR 1.40, p = 0.15), but significantly increased rates of pCR (RR 1.91, p = 0.0001). Similarly, dual HER2 blockade compared to trastuzumab alone did not improve BCS rate (RR 1.03, p = 0.84), but significantly increased rates of pCR overall (RR 1.39, p < 0.00001), in both ER+ (RR 1.72, p = 0.01) and ER- subsets (RR 1.91, p = 0.0001), with no increase in grade 3/4 toxicity (RR:1.13, p = 0.16). Dual HER-2 blockade without chemotherapy was associated with pCR in a subset (11.2% - 27%) with minimal toxicity (incidence of grade 3/4 toxicity:1-5%). Higher pCR was associated with improved DFS (RR 2.29, p = 0.006) and OS (RR 4.61, p = 0.009). Conclusions: Neither the addition of trastuzumab to chemotherapy, nor the dual-HER2 blockade compared to trastuzumab, improves rates of BCS. However,both significantly improve rates of pCR, which is associated with improved DFS and OS. Dual HER2 blockade,with endocrine therapy for ER+, could potentially lessen or even obviate the use of chemotherapy.