Safety and Pharmacokinetics of Atezolizumab Combination Treatments in Participants With HER2-Positive and HER2-Negative Breast Cancer

Atezolizumab 1200 milligrams (mg) or 840 mg (Cohort 1E only) flat dose administered via intravenous (IV) infusion on Day 1 of every 21-day cycle.

Carboplatin will be administered at an initial target of area under the curve (AUC) of 6 milligrams per milliliter\*min (mg/mL\*min) via an IV infusion on Day 1 of every 21-days for 6 cycles.

Docetaxel 75 mg/m\^2 administered via IV infusion on Day 1 every 21-days for 6 cycles.

Pertuzumab 840 mg loading dose then 420 mg administered via IV infusion on Day 1 of every 21-day cycle.

Trastuzumab 8 milligram per kilogram (mg/kg) loading dose, then 6 mg/kg administered via IV infusion on Day 1 of every 21-day cycle.

Trastuzumab emtansine 3.6 mg/kg administered via IV infusion on Day 1 of every 21-day cycle. Dose de-escalation may occur for trastuzumab emtansine, from the full trastuzumab emtansine dose at 3.6 mg/kg on Day 1 of every 21-day cycle, potentially to 3.0 mg/kg (Cohort 1C) or 2.4 mg/kg q3w (Cohort 1D).

Doxorubicin will be administered at 60 mg/m\^2 every 2 weeks as an IV bolus over 3 to 5 minutes or as an infusion over 15 to 30 minutes.

Cyclophosphamide will be administered at 600 mg/m\^2 on Day 1 of each 21 day cycle as an IV bolus over 3 to 5 minutes or as an infusion, in accordance with local policy.