Abstract PO2-18-12: Updated Results of a Phase II Study: Neoadjuvant Inetetamab Combined with Pertuzumab, Paclitaxel and Carboplatin for Locally Advanced HER2-Positive Breast Cancer

Abstract Background: Inetetamab is a neotype HER2-targeted monoclonal antibody with amino acids modified Fc segment which optimizes the antibody-dependent cellular cytotoxicity effect. However, robust evidence evaluating the combination of inetetamab combined with pertuzumab, paclitaxel and carboplatin (TCbIP) for neoadjuvant therapy is still lacking. This study aimed to evaluate the efficacy and safety of TCbIP as a neoadjuvant therapy for patients with locally advanced HER2-positive breast cancer. We now present the updated results of this trial. Methods: This phase II trial included female patients with histologically confirmed stage IIA to IIIC HER2-positive primary invasive breast cancer. Eligible patients received TCbIP treatment every three weeks for a maximum of six cycles followed by surgery. The primary endpoint was pathologic complete response (pCR, ypT0/is ypN0) rate. Key secondary endpoints included near pCR (npCR, residual breast disease 1cm) rate, objective response rate (ORR) and safety. Results: From November 2021 to July 2023, 40 patients were enrolled in the trial. One patient received one cycle of the study treatment but was lost to follow-up without surgery, and five patients received one cycle of the study treatment and were still undergoing treatment, leaving 34 patients in the intention-to-treat (ITT) population. Among these 34 patients (82.4% in stage III), 22 patients completed the study treatment and surgery (per-protocol PP population) and 12 patients were still undergoing neoadjuvant treatment. The ORR was 91.2% (31/34) in the ITT population and 86.4% (19/22) in the PP population. Among the 22 patients in the PP population, 12 patients (54.5%) achieved pCR, and18 patients (81.8%) achieved npCR. The pCR rates for patients with hormone receptor (HR) negative and positive tumors were 80.0% (8/10) and 33.3% (4/12), respectively. The most common grade 3 adverse event was neutropenia (17.6%). No significant reduction in the left ventricular ejection fraction was observed in any patient. Conclusions: Neoadjuvant therapy with TCbIP demonstrated promising efficacy and manageable toxicity in patients with HER2-positive locally advanced breast cancer. Registration number: NCT05749016 (www.clinicaltrials.gov). Citation Format: Yue Chai, Jiaxuan Liu, Mingxia Jiang, Maiyue He, Xin Wang, Yipeng Wang, Xue Yang, Jing Wang, Binghe Xu, Qiao Li. Updated Results of a Phase II Study: Neoadjuvant Inetetamab Combined with Pertuzumab, Paclitaxel and Carboplatin for Locally Advanced HER2-Positive Breast Cancer abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO2-18-12.