Four large trials evaluating adjuvant trastuzumab for HER2-positive breast cancer demonstrated significant improvements in disease-free survival (DFS; 36% to 52% reduction in DFS events) and overall survival (OS; 33% to 37% reduction in deaths). These data has led adjuvant trastuzumab becoming the foundation of care for HER2-positive early breast cancer.

The North Central Cancer Treatment Group (NCCTG) N9831 and the National Surgical Adjuvant Breast and Bowel Project (NSABP) B-31 trials assessed the efficacy and safety of adding 52 weeks of trastuzumab to standard anthracycline/taxane based chemotherapy (doxorubicin plus cyclophosphamide [AC] followed by paclitaxel). A joint analysis of data from the two studies in 2005, with a median follow-up of 2 years, demonstrated a 52% reduction in DFS event rate with the addition of trastuzumab (p <0.001) and a 33% early improvement in OS (p = 0.015). A second interim analysis with a median follow-up of 2.9 years demonstrated a continued reduction in DFS event rate and a statistically significant 35% reduction in mortality (P<0.001). The first joint analysis of N9831 arms A and C with B-31 arms 1 and 2 was based on the 3351 patients who enrolled before a pre-specified calendar date and had at least one follow-up evaluation.

In this paper, researchers present the findings of the joint analysis based on all 4045 patients enrolled onto these treatment arms before the enrollment was terminated. At 3.9 years of median follow-up, the researchers report that there continues to be a statistically significant reduction in DFS event rate in favour of the trastuzumab-containing arm (p <0.001). Similarly, there continues to be a statistically significant 39% reduction in death rate in favour of the trastuzumab-containing arm (p <0.001).

The researchers conclude that with the longest follow-up reported to date, these data demonstrate consistent DFS and OS advantages of adjuvant trastuzumab over time, which continue to outweigh the risks of adverse effects.