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.