Abstract PO4-04-02: Real-world first line use of trastuzumab biosimilar (HLX02), pertuzumab and chemotherapy for Chinese patients with HER2-positive metastatic breast cancer

Abstract Background: HLX02 (Zercepac®) is the first manufactured trastuzumab biosimilar in China. Its similar efficacy, safety, and immunogenicity compared with Herceptin was confirmed in phase III clinical trials in patients with HER2-positive advanced breast cancer. Nevertheless, the real-world evidence of HLX02 combined with pertuzumab and chemotherapy in HER2-positive advanced breast cancer in China is still warranted. Methods: In this real world observational study, patients with HER2-positive advanced breast cancer who received HLX02, pertuzuamb and chemotherapy as first line treatment at Beijing Cancer Hospital from April 2020 to April 2023 were retrospectively and prospectively included. The primary outcome was progression-free survival (PFS), and secondary outcomes included overall survival (OS), objective response rate (ORR), disease control rate (DCR) and adverse events (AEs). Results: A total of 55 patients (including one male) were included in this study and analyzed. The median age was 57 (range: 49, 62) years. Nearly one-third of tumors were estrogen receptor-positive (n=20, 36.4%). Thirty patients (54.5%) had newly-diagnosed stage IV disease. Visceral metastasis was reported in 40 patients (72.7%), most commonly observed in liver (n=22, 40%) and lung (n=19, 34.5%). Seven patients received prior anti-HER2 therapy during (neo-) adjuvant therapy (n=7, 12.7%). Taxane was the most commonly administrated chemotherapy regimen (n=51, 92.7%), including 56.4% albumin-bound paclitaxel, 20% liposomal paclitaxel and 18.2% docetaxel. Objective response was observed in 44 patients, leading to an ORR of 80%, and the DCR achieved 100%. HLX02 and pertuzumab was continued as maintenance therapy in 50 patients (90.9%), among which 17 combined with endocrine therapy (30.9%) and 6 combined with oral chemotherapy (10.9%). With a median follow-up of 9.8 months (range: 0.6-38.2). Progressive disease (PD) occurred in 12 of 55 patients (21.8%) and no deaths occurred. The median PFS was 24.8 months (95% confidence interval CI: 16.9- not estimated). The 12-month and 18-month PFS rate was 84.0% (95%CI: 72.9-96.9) and 58.8% (95%CI: 41.5 ~ 83.2), respectively. OS cannot be estimated yet due to immature data. HLX02-related diarrhea and infusion-related reaction was reported in 2 (3.6%) and 1 (1.8%) patients, respectively. LVEF values were monitored before and after drug administration, no clinical significant decline in LVEF and cardiac toxicity was observed. Conclusions: The trastuzumab biosimilar HLX02 demonstrated comparable efficacy and safety to Herceptin when combined with pertuzumab and chemotherapy for Chinese patients with HER2-positive advanced breast cancer in real world first-line treatment, which suggested that HLX02 may provide another option of Her2-targeted therapy combined with pertuzumab for Chinese patients. The benefit regarding long-term survival need to be further verified. Table 1. Effectiveness Citation Format: Ruyan Zhang, Guohong Song, Xiaoran Liu, Hui-Ping Li. Real-world first line use of trastuzumab biosimilar (HLX02), pertuzumab and chemotherapy for Chinese patients with 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 PO4-04-02.