Inclusion Criteria:

        All study parts:

          -  Participants must be willing to provide adequate archival tissue sample

          -  Participants must be willing to use highly effective birth control

          -  Participants must have adequate organ function

          -  Participants must be able to swallow capsules

        Dose escalation- Participants must have one of the following:

          -  Parts A and B: ER+ HER2- breast cancer with evidence of locally advanced unresectable
             or metastatic disease who have had the following:

          -  Part A: may have had up to 1 prior regimen of any kind for in the advanced/metastatic
             setting and no prior cyclin-dependent kinase 4/6 (CDK4/6) inhibitor therapy.

          -  Part B: may have had up to 2 prior regimens, no more than 1 of which may be endocrine
             therapy in the advanced/metastatic setting, and must have received a prior CDK4/6
             inhibitor

          -  Cohort E4: No prior everolimus.

          -  Cohort E5: No prior alpelisib and must have a phosphatidylinositol 3-kinase catalytic
             α (PIK3Cα) mutation as determined by local testing.

          -  Part C: ER+, human epidermal growth factor receptor 2 positive (HER2+) breast cancer
             with evidence of locally advanced unresectable or metastatic disease who have had at
             least 2 HER2-directed therapies for advanced disease and prior trastuzumab,
             pertuzumab, and TDM-1 required in any setting.

          -  Part D: ER+, EEC that has progressed after platinum containing chemotherapy and no
             prior fulvestrant or aromatase inhibitor therapy.

        Participants with ER+/HER2- breast cancer enrolled in this study must have had evidence of
        clinical benefit while on endocrine therapy for at least 24 months in the adjuvant setting
        or at least 6 months in the advanced/metastatic setting or have untreated de novo
        metastatic breast cancer

        Exclusion Criteria:

          -  Participants must not have certain infections such as hepatitis or tuberculosis or HIV
             that are not well controlled

          -  Participants must not have another serious medical condition

          -  Participants must not have cancer of the central nervous system that is unstable

          -  Participants must not be pregnant or breastfeeding