A Study of Ipatasertib in Combination With Paclitaxel as a Treatment for Participants With PIK3CA/AKT1/PTEN-Altered, Locally Advanced or Metastatic, Triple-Negative Breast Cancer or Hormone Receptor-Positive, HER2-Negative Breast Cancer

Inclusion Criteria:

Women or men aged =>18 years with histologically documented triple-negative breast cancer (TNBC) or HR+/HER2- adenocarcinoma of the breast that is locally advanced or metastatic and is not amenable to resection with curative intent
Eastern Cooperative Oncology Group (ECOG) Performance Status of 0 or 1
Adequate hematologic and organ function within 14 days prior to treatment initiation
Histologically documented TNBC or HR+/HER2- adenocarcinoma of the breast that is locally advanced or metastatic and is not amenable to resection with curative intent
Measurable disease according to Response Evaluation Criteria in Solid Tumors (RECIST) v1.1
Eligible for taxane monotherapy, as per local investigator assessment (e.g., absence of rapid clinical progression, life-threatening visceral metastases, or the need for rapid symptom and/or disease control which may require combination chemotherapy)
HR+/HER2- breast cancer that is not considered appropriate for endocrine-based therapy and meets one of the following: patient has recurrent disease <=5 years of being on adjuvant endocrine therapy or if patient with de novo metastatic disease have progressed within 6 months of being on first line endocrine therapy.
Consent to submit a formalin-fixed, paraffin-embedded tumor (FFPE) tissue block or freshly cut unstained, serial tumor slides from the most recently collected tumor tissue for central molecular analysis
Confirmation of biomarker eligibility using an appropriately validated molecular assay at a diagnostic laboratory, Clinically Laboratory Improvement Amendments (CLIA) or equivalently accredited i.e., valid results from either central testing or local testing of tumor tissue or blood demonstrating PIK3CA/AKT1/PTEN-altered status
For women of childbearing potential: agreement to remain abstinent (refrain from heterosexual intercourse) or use contraception and agreement to refrain from donating eggs
For men: agreement to remain abstinent (refrain from heterosexual intercourse) or use contraceptive methods and agreement to refrain from donating sperm

Exclusion Criteria:

Treatment with approved or investigational cancer therapy within 14 days prior to treatment initiation
Any previous chemotherapy for inoperable locally advanced or metastatic TNBC or HR+/HER2- adenocarcinoma of the breast (patients receiving neo/adjuvant chemotherapy eligible provided they have at least a 12 month disease-free interval)
History of or known presence of brain or spinal cord metastases
Malignancies other than breast cancer within 5 years prior to treatment initiation (except for appropriately treated carcinoma in situ of the cervix, non-melanoma skin carcinoma, or Stage I uterine cancer)
Prior treatment with an Akt inhibitor (prior PI3K or mTOR inhibitors are allowed)
History of malabsorption syndrome or other condition that would interfere with enteral absorption or results in the inability or unwillingness to swallow pills
Active infection requiring systemic anti-microbial treatment (including antibiotics, anti-fungals, and anti-viral agents)
Known human immunodeficiency virus (HIV) infection
Known clinically significant history of liver disease consistent with Child-Pugh Class B or C, including active viral or other hepatitis, current drug or alcohol abuse, or cirrhosis
Major surgical procedure, open biopsy, or significant traumatic injury within 28 days prior to initiation of treatment (or anticipated need during study)
Pregnant or breastfeeding, or intending to become pregnant during the study
Clinically significant cardiac dysfunction (including NYHA Class II/III/IV heart failure, left ventricular ejection fraction [LVEF] <50%, active ventricular arrhythmia requiring medication, history of myocardial infarction within 6 months of treatment initiation, clinically significant electrocardiogram [ECG] abnormalities).
Need for chronic corticosteroid therapy of >=10 mg of prednisone per day or an equivalent dose of other anti-inflammatory corticosteroids or immunosuppressants for a chronic disease
Unresolved, clinically significant toxicity from prior therapy, except for alopecia and Grade 1 peripheral neuropathy
Uncontrolled clinical symptoms including pleural effusion, pericardial effusion, or ascites, tumor-related pain, hypercalcemia (or symptomatic hypercalcemia requiring continued use of bisphosphonate therapy)
History of Type I or Type II diabetes mellitus requiring insulin
Grade >=2 uncontrolled or untreated hypercholesterolemia or hypertriglyceridemia
History of or active inflammatory bowel disease or active bowel inflammation
Clinically significant lung disease (including pneumonitis, interstitial lung disease, idiopathic pulmonary fibrosis, cystic fibrosis, active infection/ history of opportunistic infections)
Treatment with strong CYP3A inhibitors or strong CYP3A inducers within 2 weeks or 5 drug-elimination half-lives, whichever is longer, prior to initiation of treatment
Grade >=2 peripheral neuropathy