Phesgo

This study will evaluate the efficacy and safety of inavolisib in combination with Phesgo (pertuzumab, trastuzumab, and rHuPH20 injection for subcutaneous use) compared with placebo in combination with Phesgo, as maintenance therapy, after induction therapy in participants with previously untreated HER2-positive advanced breast cancer (ABC).

The purpose of this study is to test the safety and effectiveness of a sequence of drugs (a Taxane plus Trastuzumab plus Pertuzumab followed by Trastuzumab Deruxtecan, followed by Tucatinib plus Ado-Trastuzumab Emtansine (T-DM1), followed by Trastuzumab plus Pertuzumab plus Tucatinib) in HER2+ Breast Cancer. The study will help investigators understand whether first intensifying therapy for a specific period and then stopping treatment is safe and effective for participants. The names of the study drugs involved in this study are: * Paclitaxel (a type of anti-microtubule agent) * Docetaxel (a type of anti-microtubule agent) * Nab-Paclitaxel (a type of anti-microtubule agent) * Trastuzumab (a type of IgG1 kappa monoclonal antibody) * Pertuzumab (a type of monoclonal antibody) * Trastuzumab Deruxtecan (a type of HER2-directed antibody drug conjugate) * Tucatinib (Tyrosine Kinase HER2 Inhibitor) * Ado-trastuzumab emtansine or T-DM1 (a type of HER2-targeted antibody-drug conjugate)