A Phase Ib/II Multicenter, Open-Label, Randomized Study E...

Inclusion Criteria:

Histologically and/or cytologically confirmed adenocarcinoma of the breast that is locally advanced or metastatic.
Previously documented ER+ and HER2- tumor according to American Society of Clinical Oncology (ASCO)/ College of American Pathologists (CAP) or European Society of Medical Oncology (ESMO) guidelines or any national guidelines with criteria conforming to ASCO/CAP or ESMO guidelines.
Disease progression during or after treatment with an approved cyclin-dependent kinase 4/6 (CDK4/6) inhibitor and approved endocrine therapy (ET) in the locally advanced or metastatic setting.
Measurable or non-measurable evaluable, disease per Response Evaluation Criteria in Solid Tumors version 1.1 (RECIST v1.1).
Eastern Cooperative Oncology Group (ECOG) Performance Status of 0 or 1.
Life expectancy >= 6 months.

Exclusion Criteria:

Advanced, symptomatic, visceral spread that is at risk of life-threatening complications in the short term appropriate for treatment with cytotoxic chemotherapy at time of entry into the study, as per national or local treatment guidelines.
Have received more than one-line of therapy for locally advanced or metastatic disease.
Have received prior chemotherapy for metastatic breast cancer.
Treatment with an approved oral ET within 7 days prior to initiation of study drug; treatment with fulvestrant or an approved CDK4/6 inhibitor within 21 days prior to initiation of study drug.
Malabsorption condition or other gastrointestinal (GI) conditions/surgeries that the investigator assesses may significantly interfere with enteral absorption
History of malignancy within 3 years prior to screening, except for cancer under investigation in this study and malignancies with a negligible risk of metastasis or death.
Known allergy or hypersensitivity to any component of the study treatments.

Clinical Trial Details