Abstract PO3-01-04: Neoadjuvant compared to adjuvant chemotherapy combined with trastuzumab in patients with HER2-positive breast cancer: a register-based cohort study
Authors: Hosseini-Mellner Servah , Wickberg Åsa , Valachis Antonis , Karakatsanis Andreas 
Published: May 2024

Abstract
Introduction Neoadjuvant therapy (NAT) is considered the standard of care in patients with HER2-positive breast cancer mainly due to the possibility to adjust the post-neoadjuvant treatment based on the tumor response to NAT. However, there is no convincing evidence on a survival benefit with NAT compared to adjuvant therapy (AT) for HER2-positive breast cancer. The aim of the present study was to compare the two therapeutic strategies in a register-based cohort of Swedish patients with primary operable HER2-positive breast cancer. Method The research database BCBaSe 3.0, which is based on the Swedish National Quality breast cancer register, was used to identify patients with primary operable HER2-positive breast cancer that diagnosed between 2008 and 2020 and received either NAT or AT including chemotherapy and trastuzumab. To mitigate confounding by indication bias, propensity score matching (PSM) with 1:1 matching was applied. The effectiveness of the two therapeutic strategies was investigated through analyzing distant disease-free survival (DDFS), breast-cancer specific survival (BCSS), and overall survival (OS). Multivariate Cox regression analyses were performed for the outcomes of interest to provide Hazard Ratios (HR) and corresponding 95% Confidence Intervals (CI). Results In total, 7258 patients with primary operable HER2-positive breast cancer treated with either NAT or AT were identified, 1789 (24.6%) received NAT and 5469 (75.4%) AT. After 1:1 PSM, 1258 patients in each therapeutic strategy were available for comparisons. After a median follow-up of 63 months, no statistically significant differences between NAT and AT were observed in either outcome (HR for DDFS: 0.97; 95% CI: 0.72 – 1.30; HR for BCSS: 0.69; 95% CI: 0.45 – 1.07; HR for OS: 0.72; 95% CI: 0.50 – 1.05). In subgroup analyses, estrogen-receptor status did not impact the results that remained statistically non-significant between NAT and AT whereas in patients with clinically positive lymph node status, NAT resulted in better BCSS (HR: 0.44; 95% CI: 0.22 – 0.89) and OS (HR: 0.49; 95% CI: 0.29 – 0.90). The latter trend was not evident in patients with clinically negative lymph node status. Conclusion Our study results confirm the equivalence of NAT and AT in terms of prognosis for patients with operable HER2-positive disease and imply a potential benefit of NAT compared to AT in patients with clinically positive lymph node status. Considering the emerging treatment strategies in HER2-positive breast cancer patients treated with NAT (pertuzumab as a part of NAT, T-DM1 as post-neoadjuvant therapy) that have been shown to improve survival but are not reflected in the study cohort, NAT should be considered as the strategy with the higher possibility to improve long-term prognosis for patients with HER2-positive disease.
Citation Format: Servah Hosseini-Mellner, Åsa Wickberg, Antonis Valachis, Andreas Karakatsanis. Neoadjuvant compared to adjuvant chemotherapy combined with trastuzumab in patients with HER2-positive breast cancer: a register-based cohort study [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 PO3-01-04.