Giredestrant for Early Breast Cancer Treatment

Inclusion Criteria: * Considered appropriate for treatment with endocrine therapy (ET) * Histologically confirmed diagnosis of ER+/HER2-, Stage I-III (low-/medium-/high-risk) early breast cancer (eBC) * Documented ER+ tumor according to American Society of Clinical Oncology (ASCO)/College of American Pathologists (CAP), defined as ≥1% of tumor cells stained positive * Documented HER2- tumor according to ASCO/CAP * Postmenopausal females at the time of signing the Informed Consent Form * Documented use of a prior adjuvant aromatase inhibitor (AI) (i.e., anastrozole, exemestane, or letrozole) for a total of ≥6 months * Documented use of an adjuvant AI (i.e., anastrozole, exemestane, or letrozole) for the consecutive ≥3 months immediately prior to consent * Participant and investigator agree that current symptoms on AI are intolerable and warrant a switch in therapy to attempt sustained treatment * Documented Grade 2 or 3 adverse events, per NCI CTCAE v6.0, determined by the investigator to be associated with AI therapy's intolerance * Participant and investigator planning the first switch from an AI * Has completed the following: (neo)adjuvant chemotherapy (if administered), definitive surgery of primary breast tumor(s) and/or axillary lymph nodes dissection (ALND) and/or sentinel lymph node biopsy (SLNB) and/or radiotherapy * Eastern Cooperative Oncology Group Performance (ECOG) Performance Status 0 or 1 Exclusion Criteria: * Participation within 6 months before enrollment in any other clinical study involving an investigational adjuvant treatment including anti-cancer agents * Diagnosis of rheumatoid arthritis, psoriatic arthritis, or other inflammatory connective tissue disease * Any prior fulvestrant or any oral selective estrogen receptor degraders (SERDs) * Have active cardiac disease or history of cardiac dysfunction * Have clinically significant liver disease consistent with Child-Pugh Class B or C, including active hepatitis (e.g., hepatitis B virus \[HBV\] or hepatitis C virus \[HCV\]), current alcohol abuse, cirrhosis, or positive test for viral hepatitis * Treatment with strong CYP3A inhibitors or inducers within 14 days or 5 drug elimination half-lives (whichever is longer) prior to initiation of study treatment * Have had any serious medical condition or abnormality in clinical laboratory tests that, in the investigator's judgment, precludes an individual's safe participation in and completion of the study