Inclusion Criteria:  Participant has a histologically and/or cytologically confirmed diagnosis of estrogen receptor positive (ER+) and/or progesterone receptor positive (PgR+) breast cancer by local laboratory Participant has a PIK3CA mutation(s) present in tumor prior to enrollment  Participant has prior treatment with an endocrine-based treatment (i.e. letrozole, anastrozole, exemestane, fulvestrant or oral SERD) and may be:  relapsed with documented evidence of progression while on (neo) adjuvant endocrine- based therapy or within 12 months from completion of (neo)adjuvant endocrine-based therapy with no treatment for metastatic disease relapsed with documented evidence of progression more than 12 months from completion of (neo)adjuvant endocrine-based therapy and then subsequently progressed with documented evidence of progression while on or after only one line of endocrine-based therapy for metastatic disease newly diagnosed advanced breast cancer, then relapsed with documented evidence of progression while on or after only one line of endocrine-based therapy.  Note: Participants with newly diagnosed endocrine-based treatment naïve advanced breast cancer will NOT be included in the study.  Participants may or may not have received prior CDK4/6i therapy. If prior CDK4/6i therapy was administered, it may have been in the adjuvant or metastatic setting If female, then the participant is postmenopausal Participant has an Eastern Cooperative Oncology Group (ECOG) performance status 0 or 1 Participant has adequate bone marrow and organ function  Exclusion Criteria:  Participant who relapsed with documented evidence of progression more than 12 months from completion of (neo)adjuvant endocrine therapy with no treatment for metastatic disease Participant had more than 1 line of prior treatment in the metastatic setting Participant has received prior treatment with chemotherapy (except for neoadjuvant/adjuvant chemotherapy), any PI3K, Mammalian Target of Rapamycin (mTOR) or Protein Kinase B (Akt) inhibitor Participant has inflammatory breast cancer at screening Participants with an established diagnosis of diabetes mellitus type I or participants with type II diabetes mellitus requiring antihyperglycemic therapy Participant has a history of acute pancreatitis within 1 year of screening or a past medical history of chronic pancreatitis Participant has currently documented pneumonitis/interstitial lung disease Participant has a history of severe cutaneous reaction, such as Steven-Johnson Syndrome (SJS), erythema multiforme (EM), Toxic Epidermal Necrolysis (TEN) or Drug Reaction with Eosinophilia and Systemic Syndrome (DRESS)  Other inclusion/exclusion criteria may apply