A Study of Imlunestrant Versus Standard Endocrine Therapy in Participants With Early Breast Cancer

Inclusion Criteria:

• Have a diagnosis of ER+, HER2- early-stage, resected, invasive breast cancer withoutevidence of distant metastasis.

• Participants must have received at least 24 months but not more than 60 months ofany adjuvant ET, from time of adjuvant ET initiation.

• Participants may have received (neo) adjuvant chemotherapy and/or targeted therapywith a CDK4/6- or PARP- inhibitor.

• Must have an increased risk of disease recurrence based on clinical-pathologicalrisk features.

• Have a Performance Status of 0 or 1 on the Eastern Cooperative Oncology Group scale.

• Have adequate organ function.

Exclusion Criteria:

• Have any evidence of metastatic disease (including contralateral ALN) orinflammatory breast cancer at primary breast cancer diagnosis.

• Participants with more than a 6-month consecutive gap in therapy during the courseof prior adjuvant ET.

• Participants who have completed or discontinued prior adjuvant ET >6 months prior toscreening.

• Participants with a history of previous breast cancer are excluded, with theexception of ipsilateral DCIS treated by locoregional therapy alone ≥5 years ago.

• Pregnant, breastfeeding, or expecting to conceive or father children within theprojected duration of the trial, starting with the screening visit through 180 daysafter the last dose of study intervention.

• Participant has previously received ET of any duration for breast cancer prevention (tamoxifen or AIs) or raloxifene.

• Participants with a history of any other cancer.

• Have serious preexisting medical conditions that, in the judgment of theinvestigator, would preclude participation in this study.