Abstract PS13-17: Capecitabine maintaining treatment improves progression-free survival in metastatic breast cancer: A prospective observational study of 669 cases
Authors: Ouyang Quchang , Hu Zhe-Yu , Yang Xiaohong , Liu Liping , Li Jing , Xiao Huawu , Gao Jianxiang , Lu Jun , Wu Hui , Xie Ning , Hu Xuming , Tian Can , Shui Zhengrong , Cao Min 
Published: February 2021

Abstract
Background: Metastatic breast cancer (MBC) has poor prognosis, and the 5 yr-OS is less than 20%. Maintaining treatment post the chemotherapy could improve the OS and the life quality. However, we lack clinical consensus for the maintaining treatment. In this study, we aim to investigate the treatment outcome of capecitabine maintaining treatment. Methods: The study recruited 669 consecutive MBC patients who received chemotherapy from January 2016 through August 2019. 256 patients received capecitabine maintaining treatment after chemotherapy, including 163 patients with maintaining treatment after the first-line chemotherapy and 67 patients with maintaining treatment after the second-line chemotherapy. 413 patients did not receive capecitabine maintaining treatment after capecitabine-based chemotherapy. Kaplan-Meier curves were plotted and COX proportional hazards models with candidate risk factor analyses stratified by chemotherapy lines and maintaining treatment were assessed the impact of each candidate on progression-free survival (PFS). Circulating tumor DNA (ctDNA) analysis was performed to screen genetic aberrations that might lead to maintaining treatment response. Results: Capecitabine maintaining treatment group showed a significant improvement in PFS compared with non-maintaining group [hazard ratio = 0.53 (95% confidence interval = 0.41-0.68); log-rank test p&lt;0.0001]. The median PFS was 19.9 months (95% CI: 15.6, 22.6) and 10.4 months (95% CI: 8.5, 14.9) in capecitabine-maintaining group and non-maintaining group, respectively. The 1st line maintaining treatment could achieve an optimal PFS (median 21.3, 95% CI: 16.1, 36.3). The median PFS of 2nd and 3rd line were 17.2 months and 10.8 months, respectively. Compared to the 2nd and 3rd line therapy, the 1st line maintaining therapy could significantly improve PFS [hazard ratio = 0.66 (95% confidence interval = 0.45-0.96); log-rank test p=0.03]. In addition, compared to non-maintaining group, more maintaining group benefited from capecitabine-based chemotherapy (CR+PR+SD: 99% vs 56%, p&lt;0.0001). Patients with hormone receptor (HR)-positive would be more benefited from capecitabine-based chemotherapy. ctDNA analysis showed that in maintaining group, PIK3CA helical domain mutation (33%) and TP53 mutation (42.9%) concentrated in patients with poor PFS. Conclusion: Capecitabine maintaining treatment significant improves PFS in MBC patients. Treatment at earlier lines would be more efficient. While HR-positive patients benefited more from capecitabine-based chemotherapy, PIK3CA helical domain mutation and TP53 mutation might be responsible for the poor response to capecitabine maintaining treatment.
Citation Format: Quchang Ouyang, Zhe-Yu Hu, Xiaohong Yang, Liping Liu, Jing Li, Huawu Xiao, Jianxiang Gao, Jun Lu, Hui Wu, Ning Xie, Xuming Hu, Can Tian, Zhengrong Shui, Min Cao. Capecitabine maintaining treatment improves progression-free survival in metastatic breast cancer: A prospective observational study of 669 cases [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS13-17.