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