Abstract P1-09-02: Homologous repair deficiency (HRD) as measure to predict the effect of carboplatin on survival in the neoadjuvant phase II trial GeparSixto in triple-negative early breast cancer

Abstract

Abstract 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 (TNBC) in two large phase II studies (GeparSixto: von Minckwitz et al, Lancet Oncol 2014, CALGB 40603: Sikov WM, J Clin Oncol 2015). Participants of the GeparSixto study showed an improvement of pCR rate from 36.9 to 53.2% (p=0.005) and DFS by absolute 9% (HR 0.56 95% CI 0.33-0.96] p=0.035) with the addition of carboplatin in the TNBC subgroup. No effect was observed in the HER2-positive subgroup. We here report results on homologous repair deficiency (HRD) status in relation to pCR and DFS in the TNBC subgroup. 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. All patients were randomized 1:1 to receive concurrently carboplatin AUC 1.5-2 q1w vs no carboplatin. Carboplatin dose was reduced from AUC 2.0 to 1.5 by an amendment after 330 patients. Primary objective is pCR rate (ypT0 ypN0). Event free survival (EFS), and overall survival (OS) were secondary objectives. HR Deficiency status was assessed on FFPE material from pretherapeutic core biopsies. HR Deficiency was defined as either HRD score high or a BRCA mutation. Results HRD status was measurable in 193 of 315 TNBC patients. 101 patients of them were randomly assigned to receive carboplatin and 92 to no additional carboplatin. After median follow-up of 34.3 months 43 event free survival (EFS) events have been reported. HR deficiency was detected in 136 (70.5%) tumors of which 79 (58.1%) showed high HRD score with intact tBRCA. HR deficiency independently predicted pCR (ypT0is ypN0) (odds ratio (OR) 2.506, CI 1.243-5.051, p=0.009). Adding carboplatin to PM significantly increased the pCR rate from 36.6% to 63.2% in HR deficient tumors with intact tBRCA (p=0.018), only marginally from 61.9% to 72.7% in BRCA mutated tumors (p=0.406), and moderately from 20.0% to 40.7% in HR non-deficient tumors (p=0.086). In general, patients with HRD deficient tumors had a better ESF than non HRD deficient ones (HR 1.805 (0.985-3.309); p=0.0526). Patients with high HRD score had an insignificant trend towards an improved EFS compared to those with low HRD score (HR 1.546 (0.764-3.127) p=0.2223). HRD deficiency did not predict carboplatin effect in patients without BRCA mutation (HR 0.8617). In multivariable analysis, only therapy, clinical nodal status before treatment, and lymphocyte predominant breast cancer were significant prognostic on EFS. Conclusion Within the GeparSixto study HR deficiency (either HRD score high or BRCA mutation) was associated with a higher pCR in general and an improved EFS. The effect of carboplatin could not be predicted by HR deficiency in this relatively small study. However, the results will help to understand the role of HR deficiency and the value of the HRD score in TNBC especially in patients without BRCA mutation. Citation Format: von Minckwitz G, Timms K, Untch M, Elkin EP, Hahnen E, Fasching PA, Schneeweiss A, Salat CT, Rezai M, Blohmer J-U, Zahm D-M, Jackisch C, Gerber B, Klare P, Kümmel S, Paepke S, Schmutzler R, Chau S, Reid J, Hartman A-R, Nekljudova V, Weber KE, Loibl S. Homologous repair deficiency (HRD) as measure to predict the effect of carboplatin on survival in the neoadjuvant phase II trial GeparSixto in triple-negative early breast cancer [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P1-09-02.