9 Weeks Vs 1 Year Adjuvant Trastuzumab in Combination with Chemotherapy: Results of the Phase III Multicentric Italian Study Short-HER.

501 Background: 1-year trastuzumab with chemotherapy is the standard adjuvant treatment for HER2+ breast cancer patients (pts). The efficacy of less extended trastuzumab exposure is still under investigation. The Short-HER study is an independent, non-profit study aimed to test the non-inferiority of 9 weeks vs 1 year of adjuvant trastuzumab. Methods: This is a phase III, multicenter, Italian trial where pts with HER2+ breast cancer were randomly assigned to: Arm A (Long) AC or ECx4 followed by 4 courses of 3-weekly docetaxel in combination with trastuzumab, followed by 14 additional courses of 3-weekly trastuzumab; or Arm B (Short) 3 courses of 3-weekly docetaxel plus weekly trastuzumab for 9 doses followed by FEC x3. When indicated, radiation therapy was administered after the completion of chemotherapy. Hormonal therapy started at the completion of chemotherapy for pts with hormone receptor positive tumors. This is a non-inferiority trial with disease-free survival (DFS) as primary end-point.Overall survival (OS) is evaluated as second primary analysis outcome. The sample size of 1250 pts has been estimated based on a hazard ratio <1.29 for the short arm to be non-inferior. The definitive analysis will take place after 198 DFS events. Secondary aims include 2-yrs failure rate, cardiac toxicity, correlative biomarkers analyses. Hazard ratio for DFS and OS (90% CI) will be estimated according to the Cox model. Data will also be analyzed by the Bayesian approach. Results: from Dec-2007 to Oct-2013, 1254 pts from 82 centers have been randomized. Pts characteristics are the following: median age 55 yrs (25-78), stage I 37.3%, IIA 40%, IIB 20.6%, III 2.1%. 30% of the pts had 1-3 positive nodes, 16% >=4. Sixty-eight% of the pts had ER+ tumors. Characteristics were balanced between the two arms. At the time of this writing, 95% of the planned DFS events have been reported. 105 Grade ≥2 cardiac events have been reported, 78 in arm A (long) and 27 in arm B (short). Grade 3-4 cardiac events were 20 in arm A and 11 in arm B. Conclusions: Shorter trastuzumab administration almost halves the rate of severe cardiac toxicity. Final DFS data will be available at the time of the meeting. Clinical trial information: NCT00629278.