Statement: Only Black women are eligible for the primary trial, as long as they do not have uncontrolled or symptomatic brain metastases.
Primary_evidence: Inclusion Criteria:   Self-identified Black, African or African American women of  18 years of age with proven diagnosis of advanced adenocarcinoma of the breast (locoregionally recurrent or metastatic disease)   ER-positive and/or PgR-positive tumor based on local laboratory results   HER2-negative breast cancer based on local laboratory results (test to be used as per local practice)   Patients must be appropriate candidates for letrozole or fulvestrant therapy   Eastern Cooperative Oncology Group (ECOG) performance status 0-2   Adequate bone marrow function:   Absolute Neutrophil Count (ANC)  1,000/mm3 (1.0 x 109/L);   Platelets 100,000/mm3 (100 x 109/L);   Hemoglobin 9 g/dL (90 g/L). Exclusion Criteria:   Current use of food or drugs known to be potent inhibitors or inducers of CYP3A4   Active uncontrolled or symptomatic brain metastases. Previously treated and clinically stable, as per Investigator's judgment, brain metastases are permitted.   Previous CDK4/6 inhibitor -