Abstract S2-04: Early survival analysis of the randomized phase II trial investigating the addition of carboplatin to neoadjuvant therapy for triple-negative and HER2-positive early breast cancer (GeparSixto)

Introduction Addition of carboplatin to anthracycline/taxane-based neoadjuvant chemotherapy has shown to improve pathological complete response (pCR; ypT0 ypN0) rates in patients with triple-negative breast cancer in two large phase II studies (GeparSixto: von Minckwitz et al. Lancet Oncol 2014; CALGB 40603: Sikov et al. J Clin Oncol 2015). Participants of the GeparSixto study with triple-negative tumors showed an improvement of pCR rate from 36.9 to 53.2% by the addition of carboplatin (p=0.005); however, no statistically significant difference in pCR rate was observed in the HER2-positive subgroup (36.8 vs 32.8%, respectively). A greater benefit with carboplatin was observed in patients with BRCA mutations or a high homologous recombination deficiency (HRD score) in the tumor (pCR rate of 30% compared to 10% for patients without HRD). So far, it is unknown whether these effects on pCR translate into a survival benefit for the patients. We here report an early survival analysis of the GeparSixto study. Patients and Methods In the GeparSixto trial (NCT01426880), patients were treated for 18 weeks with paclitaxel 80mg/m2 q1w and non-pegylated-liposomal doxorubicin (NPLD) 20mg/m2 q1w. Patients with TNBC (N=315) received concurrently bevacizumab 15mg/kg i.v. q2w until surgery. Patients with HER2+ disease (N=273) received concurrently trastuzumab 6(8)mg/kg q3w and lapatinib 750mg daily. All patients were randomized 1:1 to receive concurrently carboplatin AUC 1.5-2.0 q1w vs no carboplatin, stratified by subtype (HER2+ vs TNBC). Carboplatin dose was reduced from AUC 2.0 to 1.5 by an amendment after 330 patients. Primary objective was pCR rate (ypT0 ypN0). Loco-regional invasive recurrence free survival (LRRFS), distant-disease- free survival (DDFS), invasive disease-free survival (IDFS), and overall survival (OS) were secondary objectives. Results 595 patients were recruited (8/2011 - 12/2012) in 51 German centers. 296 patients were randomly assigned to receive carboplatin and 299 to no additional carboplatin, of whom 295 and 293 started treatment, respectively. So far, 82 events have been reported after a median of 28 months follow-up. Analysis of updated events by treatment arm in the full study population as well as in the TNBC and HRD subgroups will be presented. Conclusion Even if the GeparSixto study was not powered to show carboplatin effects on survival, the expected results will help to assess the overall benefit of carboplatin in TNBC and the power of pCR to predict for DFS and OS. Citation Format: von Minckwitz G, Loibl S, Schneeweiss A, Salat CT, Rezai M, Zahm D-M, Klare P, Blohmer J-U, Tesch H, Khandan F, Fasching PA, Jakisch C, Nekljudova V, Untch M. Early survival analysis of the randomized phase II trial investigating the addition of carboplatin to neoadjuvant therapy for triple-negative and HER2-positive early breast cancer (GeparSixto). [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr S2-04.