Table 1.

Key inclusion and exclusion criteria.

Key inclusion criteria
Men or pre- or postmenopausal women aged ⩾18 years with histologically confirmed unilateral primary invasive HR+/HER2− breast cancer, with a date of initial cytological or histological diagnosis ⩽18 months prior to randomization
Complete surgical resection with microscopic margins free of tumors with available archival tumor tissue from the surgical specimen or from the diagnostic biopsy for patients who had neoadjuvant therapy and achieved a pathologic complete response
Anatomic stage group II a or III disease per the AJCC Cancer Staging Manual, 8th edition
ECOG performance status of 0 or 1
Completion of (neo)adjuvant chemotherapy (if indicated) and adjuvant radiotherapy (if indicated)
Permitted to have already received any standard (neo)adjuvant ET but must be randomized within 12 months of the initial start date of ET
Key exclusion criteria
Distant metastases of breast cancer beyond the regional lymph nodes and/or evidence of disease after curative surgery
Prior treatment with a CDK4/6 inhibitor
Prior treatment with tamoxifen, raloxifene, or aromatase inhibitors for reduction in risk of breast cancer and/or prior treatment for osteoporosis in the preceding 2 years
Prior treatment with anthracyclines at cumulative doses of ⩾450 mg/m2 for doxorubicin or ⩾900 mg/m2 for epirubicin
Clinically significant, uncontrolled heart disease and/or cardiac repolarization abnormalities
Major surgery, chemotherapy, or radiotherapy within 14 days prior to randomization

^aAll patients with stage IIB or III disease are eligible. Patients with stage IIA disease that is N0 with additional risk factors, including G3, or G2 with Ki67 ⩾ 20% or high genomic risk, and patients with stage IIA disease that is N1 are also eligible.

CDK, cyclin-dependent kinase; ECOG, Eastern Cooperative Oncology Group; ET, endocrine therapy; HER2−, human epidermal growth factor receptor 2 negative; HR+, hormone receptor positive.