Study of Efficacy and Safety of LEE011 in Postmenopausal Women With Advanced Breast Cancer

Key Inclusion Criteria:

1. Women with advanced (locoregionally recurrent or metastatic) breast cancer that was not amenable to curative therapy.
2. The patient was postmenopausal. Postmenopausal status was defined either by:

   * Prior bilateral oophorectomy
   * Age ≥60
   * Age \<60 and amenorrhea for 12 or more months (in the absence of chemotherapy, tamoxifen, toremifen, or ovarian suppression) and FSH and estradiol in the postmenopausal range per local normal range.
3. There was no prior systemic anti-cancer therapy for advanced disease.
4. The patient had a histologically and/or cytologically confirmed diagnosis of estrogen-receptor positive and/or progesterone receptor positive breast cancer by the local laboratory.
5. The patient had HER2-negative breast cancer defined as a negative in situ hybridization test or an IHC status of 0, 1+ or 2+. If IHC was 2+, a negative in situ hybridization (FISH, CISH, or SISH) test was required by local laboratory testing.
6. The patient must have had either:

   Measurable disease, i.e., at least one measurable lesion as per RECIST 1.1 criteria (Tumor lesions previously irradiated or subjected to other locoregional therapy were considered measurable if disease progression at the treated site after completion of therapy was clearly documented). OR If no measurable disease was present, then at least one predominantly lytic bone lesion must have been present (Patients with no measurable disease and only one predominantly lytic bone lesion previously irradiated were eligible if there was documented evidence of disease progression of the bone lesion after irradiation).
7. The patient had an Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1.

Key Exclusion Criteria:

1. The patient had received any CDK4/6 inhibitor.
2. The patient had received any prior systemic anti-cancer therapy (including hormonal therapy and chemotherapy) for advanced breast cancer.

   Note:
   * Patients who had received (neo) adjuvant therapy for breast cancer were eligible. If the prior neo (adjuvant) therapy included letrozole or anastrozole, the disease-free interval had to be greater than 12 months from the completion of treatment until randomization.
   * Patients who had received ≤ 14 days of letrozole or anastrozole for advanced disease prior to randomization were eligible.
   * Any prior (neo) adjuvant anti-cancer therapy had to be stopped at least 5 half-lives or 7 days, whichever was longer, before randomization.
3. The patient was concurrently using other anti-cancer therapy.
4. The patient had a concurrent malignancy or malignancy within 3 years of randomization, with the exception of adequately treated, basal or squamous cell carcinoma, non-melanomatous skin cancer, or curatively resected cervical cancer.
5. The patient had active cardiac disease or a history of cardiac dysfunction, including any of the following:

   * History of angina pectoris, symptomatic pericarditis, or myocardial infarction within 12 months prior to study entry.
   * History of documented congestive heart failure (New York Heart Association functional classification III-IV).
   * Documented cardiomyopathy.
   * The patient had a Left Ventricular Ejection Fraction (LVEF) \< 50% as determined by Multiple Gated acquisition (MUGA) scan or echocardiogram (ECHO).
   * History of any cardiac arrhythmias, e.g., ventricular, supraventricular, nodal arrhythmias, or conduction abnormality in the previous 12 months.
   * On screening, any of the following cardiac parameters: bradycardia (heart rate \< 50 at rest), tachycardia (heart rate \> 90 at rest), PR interval \> 220 msec, QRS interval \>109 msec, or QTcF \>450 msec.
   * Systolic blood pressure \>160 or \<90 mmHg.
6. The patient was currently receiving any of the following medications and could not be discontinued 7 days prior to the start of treatment:

   * Medications known to be strong inducers or inhibitors of CYP3A4.
   * Medications known to have a risk of prolonging the QT interval or inducing Torsades de Pointes.
   * Medications with a narrow therapeutic window and predominantly metabolized through CYP3A4.
   * Herbal preparations/medications.