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