THIEME 89 Primary Systemic Therapy for HER2/Neu-Positive Operable Breast Cancer Increases the Number of Breast-Conserving Surgery and Disease-Free Survival: Retrospective Cohort Analysis at Single Institution Yohana Azhar 1 , Hasrayat Agustina 2 Bethy S. Hernowo 2 1 Division Oncology, Head and Neck Surgery, Department of Surgery, Hasan Sadikin General Hospital/Faculty of Medicine Universitas Padjadjaran, Bandung, West Java, Indonesia 2 Department of Pathology Anatomy, Hasan Sadikin General Hospital/Faculty of Medicine Universitas Padjadjaran, Bandung West Java, Indonesia Address for correspondence Yohana Azhar MD, PhD, Department of Surgery, Division Oncology Head and Neck Surgery, Hasan Sadikin General Hospital/Faculty of Medicine, Universitas Padjadjaran, Pasteur No.38, Bandung, West Java 40161, Indonesia (e-mail: yohanaspbonk@gmail.com). Objective The aim of this study was to evaluate the efficacy and cardiotoxicity pro- file, and to reduce the extend of breast cancer surgery in primary systemic therapy (PST) HER2/neu–positive operable breast cancer patients. Materials and Methods A total of 152 patients diagnosed from 2010 to 2015 were included in the study. The PST consisted of a sequential regimen of taxanes and anth- racyclines plus trastuzumab. The clinical and pathological responses and the type of breast cancer surgery were evaluated and correlated with clinical and biological factors. The cardiotoxicity profile and long-term benefits were analyzed. Results The median patient age was 47 (37–67) years, with T2 and T3 67 (44.1%) and 85 (55.9%), respectively. Axillary lymph node breast cancer at diagnosis N0 was 104 (68.4%) and N1 and N2 were 28.9% and 2.6%, respectively. A total of 95.7% of patients had nonspecific type of breast cancer, 67% of tumors were hormonal receptor–neg- ative, 75.5% were grade III, 100% Ki67 > 20%, and 90% of tumors were confirmed to be HER2/neu–positive through immunohistochemistry. Following PST, pathological complete response (pCR) rate was achieved in 44.7% evaluable patients. The pCR rate was higher in HR-negative (93.1% vs. 6.9%) cancer and in grade III (86.2%) than in grade I and II (13.8%) cancer; only 75.5% of complete response (CR) on ultrasound and magnetic resonance imaging were also CR on pathology results. Breast conserv- ing surgery was performed in 41.4%. Regarding type of chemotherapy, there were no significant differences between chemotherapy with anthracycline backbone or tax- anes to achieved pathological complete response. Despite that, we were unable to demonstrate an association between pCR and better DFS with p = 0.096; HR 5.7 95.0% Abstract DOI https://doi.org/ 10.1055/s-0041-1729481 ISSN 2454-6798 ©2021. Spring Hope Cancer Foundation & Young Oncologist Group of Asia. This is an open access article published by Thieme under the terms of the Creative Commons Attribution-NonDerivative-NonCommercial-License, permitting copying and reproduction so long as the original work is given appropriate credit. Contents may not be used for commercial purposes, or adapted, remixed, transformed or built upon. (https://creativecommons.org/licenses/by-nc-nd/4.0/). Thieme Medical and Scientific Publishers Pvt. Ltd. A-12, 2nd Floor, Sector 2, Noida-201301 UP, India Asian J Oncol 2021;7:89–95. Keywords ► primary systemic therapy ► HER2/neu operable breast cancer ► breast conserving surgery ► pathological complete response ► disease-free survival Original Article Published online: 2021-04-29