Abstract PS13-01: Primary analysis of OVERSTEP: A multicenter, randomized clinical trial of capecitabine or endocrine therapy as a maintenance therapy after the 1st-line chemotherapy in hormone receptor positive and HER2-negative advanced/metastatic breast cancer

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Abstract Background: Endocrine therapy(ET) and Chemotherapy(CT) are used as standard maintenance therapy for HR+ and HER2- metastatic breast cancer(MBC) in clinical practice. There was no prospective study data on which is better. In OVERSTEP, we provide some strong evidence for clinical practice. Methods: OVERSTEP(NCT02597868) is a multicenter, randomized, open-label, prospective clinical trial that enrolled 181 patients in China. patients aged 18-70 years without chemotherapy for ABC/MBC previously, histologically confirmed metastatic HR+ and HER2- breast cancer, and ECOG performance status of 0-1. These patients were received capecitabine plus another chemotherapy drug as 1st-line salvage chemotherapy at least 4 cycles. The patients response are CR, PR and SD carried maintenance treatment next, randomly assigned (1:1) to receive either capecitabine single or endocrine therapy. Randomization was done centrally with stratification by endocrine resistance and visceral metastasis. The primary endpoint was progression-free survival(PFS) and analyses were base on all patients who received at least one dose maintenance therapy. We take superiority test in the 2 groups. Results: 136(75.14%) patients were randomized after combined chemotherapy to capecitabine single or endocrine therapy groups for maintenance treatment. 45(24.86%) patients are progress disease (PD) after combined chemotherapy. After a median follow-up of 24.3 months (IQR 20.46-37.25 ) in the endocrine maintenance therapy group and 24.1 months(IQR 20.67-36.77) in the Capecitabine maintenance therapy group ,the hazard ratio for PFS was 0.625(95%CI 0.429-0.909 P=0.013),Median PFS was 17.5 months(95%CI 11.544-23.856) in endocrine maintenance therapy group and 12,2 months(95%CI 11.170-13.230) in capecitabine maintenance therapy group. In endocrine sensitive group, the hazard ratio for PFS was 0.515(95%CI0.269-0.988 P=0.042), Median PFS was 29.3 months(95%CI 14.605-43.995) in endocrine maintenance therapy group and 14.8 months(95%CI 7.445-22.155) in capecitabine maintenance therapy group. In endocrine resistance group, the hazard ratio for PFS was 0.791(95%CI 0.499-1.253 P=0.314), Median PFS was 13.6 months(95%CI 9.111-18.089) in endocrine maintenance therapy group and 12.0 months(95%CI10.357-13.643) in capecitabine maintenance therapy group. In visceral metastasis group, the hazard ratio for PFS was 0.668(95%CI0.410-1.089 P=0.101), Median PFS was 14.3 months(95%CI 11.113-17.487) in endocrine maintenance therapy group and 11.0 months(95%CI 8.140-13.860) in capecitabine maintenance therapy group. In non-visceral metastasis group, the hazard ratio for PFS was 0.54(95%CI0.300-0.972 P=0.037), Median PFS was 25.3 months(95%CI 15.278-35.322) in endocrine maintenance therapy group and 17.0months(95%CI 10.783-23.217) in capecitabine maintenance therapy group. Conclusions: For HR+ and HER2- MBC, after 1st-line salvage combined chemotherapy, ET maintenance has a better survival benefits than CT,especially for ET-sensitive and non-visceral involved cases. So ET maintenance is the first choice for ABC/MBC after 1st-line combined chemotherapy. Citation Format: Jian Huang, Xiying Shao, Li Cai, Yanxia Shi, Zhanhong Chen, Ping Huang, Yongmei Yin, Lili Zhang, Peng Shen, Wenming Cao, Weiwu Ye, Yuan Huang, Caijin Lou, Lei Lei, Yabin Zheng, Weibin Zou, Junqing Chen, Xiaojia Wang. Primary analysis of OVERSTEP: A multicenter, randomized clinical trial of capecitabine or endocrine therapy as a maintenance therapy after the 1st-line chemotherapy in hormone receptor positive and HER2-negative advanced/metastatic breast cancer [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 PS13-01.