Abstract PO1-02-04: The efficacy of endocrine therapy during the waiting period for surgery for hormone receptor-positive breast cancer
Authors: Maeda Yuka , Naruse Saki , Isono Yuka , Sato Ayana , Matsumoto Akiko , Ikeda Tatsuhiko , Jinno Hiromitsu 
Published: May 2024

Abstract
Background: Although neoadjuvant endocrine therapy has been used to improve breast conservation rate, its prognostic relevance is unknown. The search for a valid prognostic factor equivalent to pCR in neoadjuvant chemotherapy is a current challenge in neoadjuvant endocrine therapy. In this study, we investigated the efficacy of short term neoadjuvant endocrine therapy utilizing the waiting period for surgery and the prognostic factor including Preoperative Endocrine Prognostic Index (PEPI) score. Methods: A total of 480 patients with StageⅠ-Ⅲ hormone receptor-positive, HER2-negative breast cancer was treated with endocrine therapy during the waiting period for surgery between October 2012 and December 2021. Premenopausal and postmenopausal patients received tamoxifen (TAM) and non-steroidal aromatase inhibitor (AI), respectively. The primary endpoint was change in tumor size by ultrasound and Ki67 expression before and after short term endocrine therapy. The secondary endpoint was prognosis of patients divided by PEPI score which was calculated using tumor size, lymph node metastasis, Ki67 expression, and ER Allred score. This study was approved by the institutional review board of Teikyo University. Results: Median age and tumor size of the entire 480 patients was 55 years (range, 31 - 89), 1.65 cm (range, 0.4 – 7.5), respectively. The median duration of endocrine therapy was 39 days (range, 1-90). 19 (0.3 %) pts were clinically node-positive. Of the entire 480 patients, 211 and 269 patients had TAM and AI, respectively. After short term endocrine therapy, the tumor size was significantly reduced from 1.83cm to 1.62cm in AI group (p=0.02), although TAM did not decrease the tumor size (p=0.89). The Ki67 expression was significantly decreased from 16.4% to 11.3% in TAM group (p=0.002), and from 15.9% to 6.98% in AI group (p &lt; 0.001). There were significant differences in the distribution of PEPI scores between TAM and AI group (p &lt; 0.05) (Table). At the median follow-up of 1012 days, patients with PEPI score ≥ 4 showed worse disease-free survival compared with patients with PEPI score &lt; 4 in TAM group (Figure1). Overall survival is not available because there were no deaths in TAM group. At the median observation period of 833 days, patients with PEPI score ≥ 4 showed worse disease-free survival compared with patients with PEPI score &lt; 4 in AI group (Figure2). In terms of mortality, patients with PEPI score ≥ 4 had worse overall survival than patients with PEPI score 0 and 1-3 (p=0.07). Conclusions: These results suggested that neoadjuvant endocrine therapy during the waiting period for surgery might be effective in reducing Ki67 expression level and PEPI score might be useful in predicting the prognosis of hormone receptor positive breast cancer patients.
Table. Distribution of PEPI score
Figure 1. Disease-free survival in patients treated with tamoxifen
Figure 2. Disease-free survival in patients treated with non-steroidal aromatase inhibitor
Citation Format: Yuka Maeda, Saki Naruse, Yuka Isono, Ayana Sato, Akiko Matsumoto, Tatsuhiko Ikeda, Hiromitsu Jinno. The efficacy of endocrine therapy during the waiting period for surgery for hormone receptor-positive 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 PO1-02-04.