Abstract P4-21-06: Dual HER2-blockade with pertuzumab and trastuzumab in HER2-positive early breast cancer: A subanalysis of data from the randomized phase III GeparSepto trial (2017)

Abstract Background Our recent randomized, multicenter phase III GeparSepto study (Untch M et al. Lancet Oncol 2016) found that substituting nab-paclitaxel for standard solvent-based paclitaxel significantly improved the pathologic complete response (pCR) rate in patients receiving a sequential regimen of taxane, epirubicin and cyclophosphamide as neoadjuvant treatment for high-risk primary breast cancer. Patients with HER2-positive tumors (32.8%; n=396) also received a combination of pertuzumab and trastuzumab: the present analysis focuses on efficacy and safety data from these HER2+ patients treated with the dual-blockade. Methods Patients with histologically confirmed early breast cancer (n = 1206) received either weekly paclitaxel 80mg/m2 or weekly nab-paclitaxel 150/125mg/m2, according to randomization), followed by four cycles of epirubicin 90 mg/m2 plus cyclophosphamide 600 mg/m2 q3w, with concurrent trastuzumab 6 mg/kg (loading (LD) dose 8 mg/kg) and pertuzumab 420 mg (LD 840 mg) q3w for those with HER2-positive tumors. The primary endpoint was pathologic complete response (pCR), defined as ypT0 ypN0. Results The GeparSEPTO trial included 396/1206 (32.8%) HER2+ primary breast cancer patients. 27.0% in the HER2-positive and 34.1% in the HER2-negative group had HR-negative disease. Baseline characteristics were otherwise comparable between HER2+ and HER2- patients. Higher rates of pCR were seen in HER2+, compared to HER2- tumors (57.8% vs 22.0%). The highest overall pCR rate was observed in the HER2+/HR- cohort with 71.0%; 66.7% with Pac and 74.6% with nab-Pac. In HER2+/HR+ pCR rate was 52.9% ; 49.4% with Pac and 56.4% with nab-Pac. Using the definition ypT0/is ypN0 for pCR; pCR rates were generally higher especially in the HER2+ cohort (66.2% (ypT0/is ypN0) vs 57.8% (ypT0 ypN0)) compared to 25.2% (ypT0/is ypN0) vs 22% (ypT0 ypN0)) in patients with HER2-negative tumors. The HER2+ patients experienced a significantly higher incidence of grade 3-4 adverse events 85.4% vs 78.0% in the HER2-cohort, p=0.003); grade 3-4 hematologic AEs 74.0% (HER2+) vs 69.5% (HER2-); p=0.120 with grade 3-4 anaemia 2.5% vs 0.9%; p=0.034); any grade thrombopenia 28.5% vs 21.8%; p=0.012) and febrile neutropenia 6.3 vs 3.3%; p=0.023. Any grade 3-4 non-haematological toxicities occurred in 38.4% vs 30.1%; p=0.005), with grade 3-4 diarrhea occurring in 7.6% vs 0.9%; p&amp;lt;0.001 of the patients. This had no impact on compliance. LVEF decreases from baseline were uncommon (7.6%) with 2.0% (HER2+) versus 0.4% (HER2-) of patients showing decreases to &amp;lt;50% along with a ≥10% decrease from baseline. Conclusion This is the largest cohort of patients with HER2-positive early breast cancer receiving a dual HER2-targeted neoadjuvant therapy of pertuzumab and trastuzumab, together with nab-paclitaxel or paclitaxel followed by epirubicin and cyclophosphamide. HER2+ patients experienced more noteworthy toxicity. The pCR rate were higher in the HER2+ cohort receiving the dual blockade and was highest in patients with in HER+/HR- particularly if nab-paclitaxel was substituted for paclitaxel. The trial is financially supported by Celgene and Roche. Citation Format: Loibl S, Jackisch J, Schneeweiss A, Schmatloch S, Aktas B, Denkert C, Schem C, Wiebringhaus H, Kuemmel S, Luebbe K, Warm M, Just M, Hanusch C, Hackmann J, Blohmer J-U, Clemens M, Engels K, Nekljudova V, von Minckwitz G, Untch M. Dual HER2-blockade with pertuzumab and trastuzumab in HER2-positive early breast cancer: A subanalysis of data from the randomized phase III GeparSepto trial [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 P4-21-06.