Abstract P2-03-19: The efficacy of neoadjuvant endocrine therapy during the waiting period for surgery in postmenopausal hormone receptor positive breast cancer
Authors: Maeda Yuka , Naruse Saki , Isono Yuka , Sato Ayana , Yamada Miki , Matsumoto Akiko , Ikeda Tatsuhiko , Jinno Hiromitsu 
Published: March 2023

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.
Patients and Methods: A total of 269 postmenopausal women with hormone receptor-positive, HER2-negative breast cancer was treated with endocrine therapy with non-steroidal aromatase inhibitor during the waiting period for surgery between October 2012 and November 2021. Of the entire 269 patients, 92 and 177 patients had anastrozole and letrozole, respectively. The primary endpoint was change in tumor size by ultrasound and Ki67 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, and ER Allred score. This study was approved by the institutional review board of Teikyo University.
Results: Median age was 68 years old (range, 41-89). ER and PgR was positive in 266 (98%) and 232 (86%) of the entire 269 patients, respectively. Median tumor size was 1.65 cm (range, 0.4-7.5). Seventeen (6.3%) pts were clinically node-positive. Patients with histological grade I tumor were 190 (70.6%). The median duration of endocrine therapy was 39 days (range, 2-88). Average pretreatment Ki67 expression was 10% (range, 0-90). Tumor diameter was significantly decreased to 1.43cm (range,0.45-5.83) after short-term endocrine therapy (p=0.01). The Ki67 expression was significantly decreased to 3.0% (range, 0-85) after endocrine therapy (p&lt; 0.01) and only five patients (1.9%) showed marked increase in Ki-67 expression. PEPI score 0, 1-3 and ≥ 4 was found in 83 (30.9%),147 (54.7%) and 39 patients (14.5%), respectively. After the median observation period of 928 days, patients with PEPI score ≥ 4 showed worse disease-free survival (Figure) compared with patients with PEPI score 0 and 1-3 (p=0.06). 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 the size and Ki67 expression level and PEPI score might be useful in predicting the prognosis of postmenopausal hormone receptor positive breast cancer patients.

Citation Format: Yuka Maeda, Saki Naruse, Yuka Isono, Ayana Sato, Miki Yamada, Akiko Matsumoto, Tatsuhiko Ikeda, Hiromitsu Jinno. The efficacy of neoadjuvant endocrine therapy during the waiting period for surgery in postmenopausal hormone receptor positive breast cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P2-03-19.