Abstract P5-11-11: Influence of the adjuvant hormonal therapy on hormone sensitivity and survival outcomes in ER+ and HER2−advanced breast cancer: A subgroup analysis of the JBCRG-C06 Safari study

Background: There are now many treatment options for estrogen receptor-positive (ER+) and human epidermal growth factor receptor 2-negative (HER2−) advanced breast cancer (ABC). However, there are few reports indicating the optimal treatment sequence for this disease. Information to predict response to treatment is vital for personalized therapy and determining the most beneficial approach for individual patients. In this study, we attempted to determine predictive factors of response to hormonal therapy and survival outcomes using the large-scale databases constructed in the Safari study (UMIN000015168), a retrospective, multicenter cohort study involving 1,072 Japanese patients receiving fulvestrant 500mg for ER+ ABC. We examined the association between clinicopathological factors and time to failure (TTF) of fulvestrant in Japanese ABC patients. Methods: Among 1072 patients, 247 patients were selected for this study. Inclusion criteria was as follows: 1) patients treated with either SERM or AI in the adjuvant setting (AS) with known starting and finishing date of the treatment (patients relapsed on adjuvant treatment were excluded), 2) patients treated with SERM, AI and SERD in the metastatic setting (MS) as the first and the second line treatment. Influence of the adjuvant hormonal therapy on the TTF of the first line and the second line treatment and overall survival (OS) was assessed. Cox proportional hazards model was used for this analysis. Results: Patients treated with SERM in AS had significantly longer TTF of 1st line and 1st+2nd line of hormonal therapy in MS (1st line: HR 1.519, 95% CI 1.04-2.218, p=0.0307, 1st+2nd line: HR 2.372, 95% CI 1.584-3.551, p Conclusions: Interestingly, once AI-treated patients in AS have relapsed, their hormone sensitivity is lower and survival outcomes are worse compared with SERM-treated patients in AS in this cohort. Our results have consistency with the results of ABCSG-12 trial showing a pronounced higher risk of death for anastrozole-treated patients (Annals of Oncology 26: 313–320, 2015). Since it is a cohort of selected patients who were successfully treated with fulvestrant, prospective analysis would be therefore warranted. Citation Format: Takahiro Nakayama, Hidetoshi Kawaguchi, Norikazu Masuda, Kenjiro Aogi, Keisei Anan, Yoshinori Ito, Shoichiro Ohtani, Nobuaki Sato, Shigehira Saji, Toshimi Takano, Eriko Tokunaga, Seigo Nakamura, Yoshie Hasegawa, Masaya Hattori, Tomomi Fujisawa, Satoshi Morita, Miki Yamaguchi, Hiroko Yamashita, Toshinari Yamashita, Yutaka Yamamoto, Daisuke Yotsumoto, Masakazu Toi, Shinji Ohno. Influence of the adjuvant hormonal therapy on hormone sensitivity and survival outcomes in ER+ and HER2−advanced breast cancer: A subgroup analysis of the JBCRG-C06 Safari study [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P5-11-11.