To Evaluate the Safety, Tolerability, and Pharmacokinetics of Inavolisib Single Agent in Participants With Solid Tumors and in Combination With Endocrine and Targeted Therapies in Participants With Breast Cancer

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