Long-term outcomes of dual vs single HER2-directed neoadjuvant therapy in NSABP B-41

Background The primary aim of this randomized neoadjuvant trial in operable, HER2-positive breast cancer, was to determine the efficacy on pathologic complete response (pCR) of substituting lapatinib (L) for trastuzumab (T) or adding L to T, in combination with weekly paclitaxel (WP) following AC. Results on pCR were previously reported. Here, we report data on planned secondary endpoints, recurrence-free interval (RFI) post-surgery, and overall survival (OS). Methods All patients received standard AC q3 weeks × 4 cycles followed by WP (80 mg/m 2 ) on days 1, 8, and 15, q28 days × 4 cycles. Concurrently with WP, patients received either T (4 mg/kg load, then 2 mg/kg) weekly until surgery, L (1250 mg) daily until surgery, or weekly T plus L (750 mg) daily until surgery. Following surgery, all patients received T to complete 52 weeks of HER2-targeted therapy. 522 of 529 randomized patients had follow-up. Median follow-up was 5.1 years. Results RFI at 4.5 years was 87.2%, 79.4% ( p = 0.34; HR = 1.37; 95% CI 0.80, 2.34), and 89.4% ( p = 0.37; HR = 0.70; 0.37, 1.32) for arms T, L, and TL, respectively. The corresponding five-year OS was 94.8%, 89.1% ( p = 0.34; HR = 1.46; 0.68, 3.11), and 95.8% ( p = 0.25; HR = 0.58; 0.22, 1.51), respectively. Patients with pCR had a much better prognosis, especially in the ER-negative cohort: RFI ( HR = 0.23, p < 0.001) and OS ( HR = 0.28, p < 0.001). Conclusions Although pCR, RFI, and OS were numerically better with the dual combination and less with L, the differences were not statistically significant. However, achievement of pCR again correlated with improved outcomes, especially remarkable in the ER-negative subset. Clinical trials registration NCT00486668