The nsabp B31 protocol (Figure 1) randomized 1736 axillary node–positive, HER2-positive breast cancer patients to 4 cycles of standard doxorubicin and cyclophosphamide (ac) followed by 4 cycles of paclitaxel administered every 3 weeks (ac–p), or the same chemotherapy with weekly trastuzumab starting concurrently with the paclitaxel (ac–ph). This evidence concerns the gene ERBB2 and breast cancer.