• Participants with proven diagnosis of adenocarcinoma of the breast with evidence of either locally advanced disease not amenable to resection or radiation therapy with curative intent or metastatic disease not amenable to curative therapy.

• Participants must be appropriate candidates for endocrine monotherapy

• Participants must have measurable disease or bone only disease with evaluable lesions

• Female or male participants age ≥ 18 years; female participants must be postmenopausal women, and male participants must not allow pregnancy with their sperm (abstain, do not donate sperm, et cetera).

• Participants must have ER+ and HER2- tumor status

• Participants must have previously received at least one and no more than two lines of endocrine therapy for advanced/metastatic breast cancer and meet additional previous treatment criteria.

• Participants must have received prior treatment with a CDK4/6 inhibitor in combination with either fulvestrant or an aromatase inhibitor (AI) for advanced/metastatic breast cancer (mBC).

• Participants may have received no more than one line of chemotherapy in the advanced/metastatic setting.