Abstract PO1-04-05: Effectiveness and safety of inetetamab + pyrotinib + vinorelbine in ≥second-line treatment of HER2-positive metastatic breast cancer

Abstract Background: In real-world settings, Patients with HER2-positive metastatic breast cancer (MBC) who cannot receive antibody-drug conjugates (ADCs) as standard second-line therapy due to cost–benefit ratios and who have no preferred options as ≥third-line regimen by NCCN guidelines, require new regimens to meet their clinical needs. This study aims to explore the effectiveness and safety of inetetamab + pyrotinib + vinorelbine for ≥second-line treatment of HER2-positive MBC. Methods: Patients with HER2-positive MBC who received ≥second-line treatment at our hospital from June 2020 to December 2022 were enrolled. Progression-free survival (PFS), objective response rate (ORR), clinical benefit rate (CBR) and adverse reactions were assessed. Patients received inetetamab + pyrotinib + vinorelbine until disease progression or unacceptable toxicity were evaluated every two cycles according to the RECIST 1.1 criteria. Results: 89 patients were included based on the inclusion and exclusion criteria. Among them, 45 patients received second-line treatment who couldn't use T-DM1 or T-DXd, and 44 patients received ≥third-line treatment. The median PFS of the second-line treatment subgroup was 17months, the ORR and CBR were 60.0% and 86.7%, respectively, which were significantly higher than those in the ≥third-line treatment subgroup and numerically superior to T-DM1 as a second-line treatment option. Additionally, the ORR and CBR of patients with baseline brain metastasis who did not receive radiotherapy were 27.3% and 72.7%, respectively. The most common adverse events observed were leukopenia (37.1%), neutropenia (42.7%), anemia (34.8%) and diarrhea (67.4%). The incidence of grade 3-4 leukopenia, neutropenia, anemia and diarrhea were 11.2%, 15.7%, 55.6% and 27.0%, respectively. A total of 8 patients (8.9%) discontinued medication due to adverse reactions. Conclusions: Inetetamab + pyrotinib + vinorelbine demonstrates good efficacy and controllable toxicity as a second-line treatment for HER2-positive MBC. This therapeutic regimen provides a viable alternative option for patients who are unable to receive ADCs as the second-line treatment. Citation Format: Fan Wu, Mulan Chen, Weiwei Huang, Lili Wang, Nani Li, Xiufeng Wu, Xinhua Chen, Yi Hong, Lin Lin, Kan Chen, Jian liu. Effectiveness and safety of inetetamab + pyrotinib + vinorelbine in ≥second-line treatment of HER2-positive metastatic 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 PO1-04-05.