Abstract:ObjectiveTo investigate the efficacy and adverse events of the biosimilar of trastuzumab (H) (Zercepac?) single target or Zercepac? and pertuzumab (P) dual target combined with chemotherapy [taxanes （T） and platinum (C)] in neoadjuvant therapy of human epidermal growth factor receptor-2(HER-2) positive breast cancer. Methods A retrospective analysis was applied to collect clinicopathological data from 48 cases of HER-2 positive breast cancer who received Zercepac? alone or Zercepac? and pertuzumab combined with chemotherapy during neoadjuvant therapy followed by breast surgery in Nanjing Drum Tower Hospital, the Affiliated Hospital of Nanjing University Medical School from November 2020 to September 2021. The Miler-Payne (MP) grading system and the Response Evaluation Criteriain Solid Tumours (RECIST) version 1.1 were performed to evaluate the pathological and clinical efficacy, respectively. Adverse reaction evaluations were carried out in accordance with Common Terminology Criteria for Adverse Events (CTCAE) version 5.0. The difference between pathological complete remission (pCR) group and non-pCR group was analyzed, and the factors influencing the pCR rate of HER-2 positive breast cancer after neoadjuvant therapy were analyzed. Results Of total 48 patients, 47 (97.9%) patients were invasive breast carcinoma of no special type, and only 1 case(2.1%) was invasive micropapillary carcinoma(IMPC). There were 39 cases (81.2%) treated with Zercepac? combined with pertuzumab and 9 cases (18.8%) treated with Zercepac? alone. There was significant difference in clinical stage between pCR group and non-pCR group (P<0.05). The MP grade of pCR group was significantly higher than that of non-pCR group (P<0.01), while the pCR rate of double target was significantly higher than that of single target (69.2% vs 22.2%, P<0.05). Single target and high clinical stage were independent risk factors affecting pCR rate after neoadjuvant therapy. Among the adverse events, the incidence of hair loss was the highest (91.7%). In cardiovascular adverse events, 4 patients had prolonged QT interval recorded by ECG, and 3 patients had different degrees of conduction block. Conclusion As a biosimilar of trastuzumab, Zercepac? is safe and effective during neoadjuvant therapy (TCH or TCHP) for HER-2-positive breast cancer, and the dual-target therapy is significantly better than single-target treatment.