9 weeks vs 1 year adjuvant trastuzumab in combination with chemotherapy: final results of the phase III randomized Short-HER study.

Background: Chemotherapy plus 1-year trastuzumab is the standard adjuvant treatment for HER2-positive breast cancer. The efficacy of less extended trastuzumab exposure is under investigation. The Short-HER study was aimed to assess the non-inferiority of 9 weeks vs 1 year of adjuvant trastuzumab combined with chemotherapy.

Patients and methods: HER2-positive breast cancer patients with node-positive or, if node negative, with at least one risk factor (pT > 2cm, G3, lympho-vascular invasion, Ki-67>20%, age ≤35 years, or hormone receptor negativity) were randomly assigned to receive sequential anthracycline-taxane combinations plus 1-year trastuzumab (arm A, long) or plus 9-weeks trastuzumab (arm B, short). This study was designed as a non-inferiority trial with disease-free survival (DFS) as primary end-point. A DFS Hazard Ratio (HR) <1.29 was chosen as the non-inferiority margin. Analyses according to the frequentist and Bayesian approach were planned. Secondary endpoints included 2-year failure rate and cardiac safety.

Results: 1254 patients from 82 centers were randomized (arm A, long: n = 627; arm B, short: n = 626). Five-year DFS is 88% in the long and 85% in the short arm. The HR was 1.13 (90%CI 0.89;1.42), with the upper limit of the CI crossing the non-inferiority margin. According to the Bayesian analysis, the probability that the short arm is non-inferior to the long one is 80%. The 5-yr OS is 95.2% in the long and 95.0% in the short arm (HR 1.07, 90%CI0.74;1.56). Cardiac events are significantly lower in the short arm (risk-ratio 0.33, 95%CI0.22;0.50, p < 0.0001).

Conclusions: This study failed to show the non-inferiority of a shorter trastuzumab administration. 1-year trastuzumab remains the standard. However, a 9-week administration decreases the risk of severe cardiac toxicity and can be an option for patients with cardiac events during treatment and for those with a low risk of relapse.