Abstract P2-08-02: Progression-free survival results in patient subgroups from a Phase 3 randomized trial of fulvestrant 500 mg vs anastrozole for hormone receptor-positive advanced breast cancer (FALCON)

Abstract

Abstract BACKGROUND Improved efficacy was suggested for fulvestrant 500 mg, a selective estrogen receptor degrader (SERD), vs anastrozole as first-line treatment for hormone receptor-positive locally advanced or metastatic breast cancer (LA/MBC) in the open-label Phase 2 FIRST trial. The Phase 3, randomized, double-blind, multicenter FALCON trial (NCT01602380) compared fulvestrant 500 mg with anastrozole 1 mg in patients with hormone receptor-positive LA/MBC who had not received prior hormonal therapy. The primary endpoint of the study was met, such that there was a statistically significant improvement in progression-free survival (PFS) for fulvestrant 500 mg vs anastrozole. We present an analysis of PFS for pre-specified patient subgroups in the FALCON trial. METHODS Eligible patients had ER and/or progesterone receptor (PgR)-positive breast cancer, WHO performance status 0–2 and ≥1 measurable/non-measurable lesion(s). Patients were randomized (1:1) to receive fulvestrant 500 mg (IM on Days 0, 14, 28, and each 28 days thereafter) or anastrozole 1 mg daily. The primary endpoint was PFS, assessed via RECIST 1.1, surgery/radiotherapy for disease worsening, or death (any cause). PFS was evaluated in patient subgroups defined by pre-specified baseline covariates. The consistency of effect across patient subgroups was assessed via hazard ratios and 95% confidence intervals using a log-rank test. RESULTS Overall, 462 patients were randomized to treatment: 230 received fulvestrant 500 mg and 232 received anastrozole. PFS outcomes in each patient subgroup are presented in the Table. CONCLUSIONS This analysis of patient subgroups from the FALCON trial suggests that treatment effects were largely consistent across the subgroups analyzed with some possible exceptions (e.g. patients with visceral vs non-visceral disease). Further work is ongoing to understand the possible treatment effect in these subgroups. PFS in pre-specified patient subgroupsSubgroup Number of patients (%) with event Hazard ratio (95% CI) Fulvestrant 500 mg n=230 Anastrozole n=232 Breast cancer type Locally advanced11/28 (39.3%)14/32 (43.8%)0.79 (0.36, 1.73)Metastatic132/202 (65.3%)152/200 (76.0%)0.78 (0.62, 0.99)Prior chemotherapy for LA/MBC Yes31/36 (86.1%)33/43 (76.7%)1.08 (0.66, 1.77)No112/194 (57.7%)133/189 (70.4%)0.75 (0.59, 0.97)Geographic regiona US/Canada16/25 (64.0%)19/24 (79.2%)0.66 (0.34, 1.30)Non-US/Canada127/205 (62.0%)147/208 (70.7%)0.81 (0.64, 1.03)Measurable disease Yes124/193 (64.2%)143/196 (73.0%)0.76 (0.60, 0.97)No19/37 (51.4%)23/36 (63.9%)0.99 (0.53, 1.82)ER-positive and PgR-positive Yes103/175 (58.9%)127/179 (70.9%)0.73 (0.56, 0.94)No40/55 (72.7%)39/53 (73.6%)1.04 (0.67, 1.62)Bisphosphonate use at baseline Yes44/61 (72.1%)53/62 (85.5%)0.69 (0.46, 1.03)No99/169 (58.6%)113/170 (66.5%)0.82 (0.63, 1.07)Visceral disease Yes92/135 (68.1%)87/119 (73.1%)0.99 (0.74, 1.33)No51/95 (53.7%)79/113 (69.9%)0.59 (0.42, 0.84)ªData for Asia/non-Asia subgroups are presented in a separate abstract Citation Format: Robertson JFR, Noguchi S, Shao Z, Grinsted LM, Fazal M, Ellis MJ. Progression-free survival results in patient subgroups from a Phase 3 randomized trial of fulvestrant 500 mg vs anastrozole for hormone receptor-positive advanced breast cancer (FALCON) [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P2-08-02.