Inclusion Criteria:

          -  Evaluable or measurable disease per RECIST, Version 1.1 (measurable disease only for
             Arm D)

          -  Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1

          -  Life expectancy of greater than or equal to (≥) 12 weeks

          -  Adequate hematologic and organ function, including blood counts, liver and kidney
             function

        Stage I Arm A (Inavolisib):

        - Locally advanced, recurrent, or metastatic, PIK3CA mutant, incurable solid tumor
        malignancy, including breast cancer

        Stages I and II, Arms B and C:

        - Postmenopausal female participants with locally advanced or metastatic PIK3CA-mutant
        HR+/HER2- breast cancer

        Stage II, Arms D, E, or F:

        - Female participants with locally advanced or metastatic PIK3CA-mutant HR+/HER2- breast
        cancer

        Stage II Arm D:

        - Prior treatment with CDK4/6 inhibitor

        Stage II Arm G:

          -  Female participants with locally advanced or metastatic PIK3CA-mutant HER2+ breast
             cancer

          -  Left ventricular ejection fraction 50% or greater

        Stages I and II:

        - All participants must provide tumor tissue from the primary or metastatic tumor site
        obtained from a prior or new biopsy or surgical procedure for detection of PIK3CA mutation
        by central laboratory test.

        Exclusion Criteria:

          -  Metaplastic breast cancer

          -  History of leptomeningeal disease

          -  Type 1 or 2 diabetes requiring anti-hyperglycemic medication

          -  Inability or unwillingness to swallow pills

          -  Malabsorption syndrome or other condition that would interfere with enteral absorption

          -  Known and untreated, or active central nervous system metastases

          -  Uncontrolled pleural effusion or ascites

          -  Any active infection that could impact patient safety or serious infection requiring
             intravenous antibiotics

          -  History of other malignancy within 5 years, except for treated carcinoma in situ of
             the cervix, non-melanoma skin carcinoma, or Stage I uterine cancer

          -  History of or active ventricular dysrhythmias or congestive heart failure requiring
             medication or symptomatic coronary heart disease

          -  Congenital long QT syndrome, prolonged QT interval, or family history of sudden
             unexplained death or long QT syndrome

        Stage II Arms B, C, D, and E only:

          -  Prior treatment with >1 chemotherapy regimen for metastatic disease

          -  Prior treatment with PI3K inhibitor

          -  History of significant toxicity related to mTOR inhibitor requiring treatment
             discontinuation

        Stage II Arms B and E only:

        - Prior CDK4/6 inhibitor treatment

        Stage II Arm G only:

          -  Current uncontrolled hypertension or unstable angina

          -  History of congestive heart failure, serious cardiac arrhythmia, or recent myocardial
             infarction

          -  Prior ejection fraction decrease on trastuzumab

          -  Prior cumulative doxorubicin greater than 360 mg/m2

          -  Symptomatic active lung disease

          -  History of significant toxicity related to trastuzumab and/or pertuzumab requiring
             discontinuation of treatment