Inclusion criteria: * Has a diagnosis of invasive breast carcinoma with estrogen receptor positive (ER+)/human epidermal growth factor receptor negative (HER2-) that is a locally advanced disease not susceptible to resection or metastatic disease not treatable with curative intent. * Has documented radiographic confirmation of disease progression during or after the last endocrine therapy (ET) administered. * Provides additional tissue from the same sample used to determine ER and HER2 status locally. * Has received ET in the non-curative setting and has 1) Radiographic progression of disease in 12 months or more of ET in combination with CDK4/6 inhibitor in the non-curative setting or 2) Has received at least 2 lines of ET in the non-curative setting, including CDK4/6 inhibitor, where the CDK4/6 inhibitor was discontinued due to intolerance. * Has an Eastern Cooperative Oncology Group (ECOG) functional status of 0 or 1 assessed within 7 days of randomization. * Participants who have AD due to previous anticancer therapies must have recovered to ≤Grade 1 or baseline. Participants with endocrine-related AD who are receiving appropriate hormone replacement therapy or participants who have neuropathy ≤ Grade 2 are eligible. * Participants who are positive for hepatitis B surface antigen (HBsAg) are eligible if they have received antiviral therapy against the hepatitis B virus (HBV) for at least 4 weeks prior to the first dose of the study intervention and have an undetectable HBV viral load prior to randomization. Exclusion criteria: * Has breast cancer amenable to curative treatment. * You cannot receive any of the endocrine therapies (ETs) (i.e., fulvestrant or exemestane). * Has known difficulty tolerating oral medications, is unable to swallow orally administered medications, or has conditions that could affect the absorption of oral medications, such as uncontrolled nausea or vomiting (i.e., CTCAE = Grade 3 despite antiemetic therapy), ongoing gastrointestinal obstruction, motility disorder, malabsorption syndrome, or previous gastric bypass. * Has advanced symptomatic/metastatic visceral dissemination with risk of rapidly progressing to life-threatening complications. * Has active disease, bleeding diathesis, or is taking oral vitamin K antagonist medication * Has a history of non-infectious pneumonitis/interstitial lung disease, including radiation pneumonitis requiring steroids, or has current pneumonitis/interstitial lung disease * Has a known (harmful or suspected) BRCA germline mutation and has received prior treatment with poly-ADP ribose polymerase (PARP) inhibition, either in the adjuvant or metastatic setting * Has previously received fulvestrant in the adjuvant, locally advanced unresectable, or metastatic setting * Has received any line of cytotoxic chemotherapy or PARP inhibitor in the advanced/metastatic unresectable or non-curative setting * Has previously received radiotherapy for disease not affecting the central nervous system (CNS) or required corticosteroids for radiation-related toxicities, including radiation pneumonitis, within 14 days of the first dose of the study intervention * Is currently Receiving a potent CYP3A4 inhibitor or inducer that cannot be discontinued for the duration of the study * Has received prior systemic anticancer therapy, including investigational agents, within 4 weeks prior to randomization * Has received a live or attenuated vaccine within 30 days prior to the first dose of the study intervention * Has concurrent active hepatitis B virus and hepatitis C virus infection * Has clinically significant heart disease, including unstable angina, acute myocardial infarction within 6 months of day 1 of study medication administration, or New York Heart Association class III or class IV congestive heart failure * Has not adequately recovered from major surgery or has ongoing surgical complications