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 without evidence of distant metastasis.
• Participants must have received at least 24 months but not more than 60 months of any adjuvant ET, from time of adjuvant ET initiation.
• Participants may have received (neo) adjuvant chemotherapy and/or targeted therapy with a CDK4/6- or PARP- inhibitor.
• Must have an increased risk of disease recurrence based on clinical-pathological risk 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) or inflammatory breast cancer at primary breast cancer diagnosis.
• Participants with more than a 6-month consecutive gap in therapy during the course of prior adjuvant ET.
• Participants who have completed or discontinued prior adjuvant ET >6 months prior to screening.
• Participants with a history of previous breast cancer are excluded, with the exception of ipsilateral DCIS treated by locoregional therapy alone ≥5 years ago.
• Pregnant, breastfeeding, or expecting to conceive or father children within the projected duration of the trial, starting with the screening visit through 180 days after 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 the investigator, would preclude participation in this study.