A Study to Test Inavolisib Treatments in Participants With Early-Stage, PIK3CA-Mutated Breast Cancer

Inclusion Criteria:

* Histologically confirmed operable or inoperable invasive Stage II-III BC according to American Joint Committee on Cancer (AJCC) TNM staging classification
* Candidate for neoadjuvant treatment and considered appropriate for endocrine combination therapy
* Willingness to undergo breast surgery (mastectomy or breast-conserving surgery) after neoadjuvant treatment (unless inoperable)
* Documented ER-positive tumor in accordance with current American Society of Clinical Oncology (ASCO)/College of American Pathologists (CAP) guidelines
* Documented HER2-negative tumor in accordance with current ASCO/CAP guidelines
* Documented Ki-67 score \>=5% as per local assessment
* Confirmed PIK3CA mutation

Exclusion Criteria:

* Stage IV (metastatic) BC
* Inflammatory BC (cT4d)
* Bilateral invasive BC
* History of ductal carcinoma in situ or lobular carcinoma in situ if they have received any systemic therapy for treatment or radiation therapy to the ipsilateral breast
* Previous systemic or local treatment for the primary BC currently under investigation (including excisional biopsy or any other surgery of the primary tumor and/or axillary lymph nodes, and sentinel lymph node biopsy, radiotherapy, cytotoxic, and endocrine treatments)
* Type 2 diabetes requiring ongoing systemic treatment at the time of study entry; or any history of Type 1 diabetes