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

Inclusion Criteria:

Patient has advanced (locoregionally recurrent or metastatic) breast cancer not amenable to curative therapy
Patient is premenopausal or perimenopausal at the time of study entry
Patients who received (neo) adjuvant therapy for breast cancer are eligible
Patient has a histologically and/or cytologically confirmed diagnosis of estrogen-receptor positive and/or progesterone receptor positive breast cancer
Patient has HER2-negative breast cancer
Patient must have either measurable disease or If no measurable disease is present, then at least one predominantly lytic bone lesion
Patient has an Eastern Cooperative Oncology Group (ECOG) performance status 0 or 1
Patient has adequate bone marrow and organ function

Exclusion Criteria:

Patient who has received a prior CDK4/6 inhibitor
Patient is postmenopausal
Patients who currently have inflammatory breast cancer at screening.
Patients who received any prior hormonal anti-cancer therapy for advanced breast cancer, except for ≤ 14 days of tamoxifen or NSAI ± goserelin for advanced breast cancer prior to randomization.
Patient has a concurrent malignancy or malignancy within 3 years of randomization, with the exception of adequately treated basal cell skin carcinoma, squamous cell skin carcinoma, non-melanomatous skin cancer or curatively resected cervical cancer.
Patient with CNS metastases.
Patient has active cardiac disease or a history of cardiac dysfunction
Patient is currently using other antineoplastic agents
Patient is pregnant or nursing or physiologically capable of becoming pregnant and not using highly effective contraception

Other protocol-defined Inclusion/Exclusion may apply.