Fulvestrant most effective in patients without visceral metastases

Up to 75% of breast cancers express the oestrogen receptor or progesterone receptor (are hormone-receptor [HR]–positive). First-line treatment recommendations for postmenopausal women with HR-positive locally advanced or metastatic breast cancer includes endocrine therapy with a third-generation aromatase inhibitor (anastrozole, letrozole, or exemestane) or tamoxifen. In HR-positive disease, third-generation aromatase inhibitors have increased efficacy compared with tamoxifen in terms of time to progression.

Fulvestrant is a selective oestrogen receptor degrader (SERD) that blocks oestrogen receptor function by inducing oestrogen receptor degradation. The phase III, randomized, double-blind, multicenter FALCON-trial compared fulvestrant (500 mg IM on Days 0, 14, 28, and each 28 days thereafter) with anastrozole ( 1 mg) in 462 patients with locally advanced/metastatic HR-positive breast cancer who had not received any prior hormonal therapy.

Results on the primary endpoint of the study, progression-free survival, were presented at the 2016 ESMO Congress in Copenhagen (October7-11) and published recently in The Lancet.¹ In summary, after a median follow-up of 25 months, patients treated with fulvestrant had a statistically significant 21% improvement in progression-free survival compared to those treated with anastrozole: 16,6 months (95% CI 13,83–20,99) versus 13,8 months (95% CI 11,99–16,59), HR 0,797, 95% CI 0,637–0,999, P = 0,048.

At the 2016 San Antonio Breast Cancer Conference John Robertson presented an analysis of progression-free survival data of various patient subgroups defined by pre-specified baseline covariates.² Treatment effects on progression-free survival were largely consistent across these subgroups, with the following exceptions: patients with previous chemotherapy for locally advanced or metastatic disease, patients with non-measurable disease, patients who were not oestrogen receptor-positive and progesterone receptor-positive at baseline, and patients with visceral disease (see keyslides for more details on other subgroups). For patients with non-visceral disease, the HR was 0,59 (95% CI 0,42–0,84), with a median progression-free survival of 22,3 months (95% CI 16,62–32,79) in the fulvestrant group versus 13,8 months (11,04–16,59) in the anastrozole group. In the visceral disease subgroup, the HR was 0,99 (0,74–1,33), with median progression-free survival of 13,8 months (11,04–16,53) in the fulvestrant group versus 15,9 months (11,27–16,89) in the anastrozole group. Further work is ongoing to understand the possible treatment effect in these subgroups.

References

1. John F R Robertson JFR, Bondarenko IM, Trishkina E,et al. Fulvestrant 500 mg versus anastrozole 1 mg for hormone receptor-positive advanced breast cancer (FALCON): an international, randomised, double-blind, phase 3 trial. The Lancet 2016, on line first (November 29).
2. Robertson JFR FR, Noguchi S, Shao Z, et al. 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). Poster presentation at the San Antonio Breast Cancer Congress 2016, abstract P2-08-02.