Study of Efficacy and Safety in Premenopausal Women With Hormone Receptor Positive, HER2-negative Advanced Breast Cancer

The purpose of this study was to determine whether treatment with tamoxifen or a non-steroidal aromatase inhibitors (NSAI) + goserelin + LEE011 prolonged progression-free survival (PFS) compared to treatment with tamoxifen or a NSAI + goserelin + placebo in premenopausal women with hormone receptor positive (HR+), human epidermal growth factor receptor 2 negative (HER2-) advanced breast cancer.

This was a randomized, Phase III, double-blind, global study comparing the treatment efficacy and safety of ribociclib + goserelin + tamoxifen or a NSAI (letrozole or anastrozole) versus placebo + goserelin + tamoxifen or a NSAI in premenopausal women with HR+, HER2- advanced breast cancer.

Eligible participants were randomized in a 1:1 ratio to either the ribociclib arm or the placebo arm. Study treatment continued until disease progression, unacceptable toxicity, death, or discontinuation for any other reason.

Participants who discontinued treatment due to reasons other than disease progression or withdrawal of consent for efficacy follow-up continued to be monitored until disease progression, death, withdrawal of consent, loss to follow-up, or subject/guardian decision (post-treatment efficacy follow-up).

All participants who discontinued treatment were followed for survival until the predetermined number of overall survival (OS) events was reached.

Following the final OS analysis (performed when approximately 189 deaths were recorded) and with protocol amendment 6 (dated 18-Jul-2019), participants and investigators were unblinded and those participants in the placebo arm had the opportunity to cross-over to the ribociclib arm to receive ribociclib + goserelin + NSAI. Cross-over was optional and was conducted at the investigator's discretion and upon participant consent.