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.