Inclusion Criteria:

          -  Confirmed diagnosis of HER2-positive breast cancer, and hormonal and PD-L1 status, as
             documented through central testing of a representative tumor tissue specimen

          -  Primary breast tumor size of > 2 cm by any radiographic measurement

          -  Stage at presentation: T2-T4, N1-N3, M0 as determined by AJCC staging system, 8th
             edition

          -  Pathologic confirmation of nodal involvement with malignancy must be determined by
             fine needle aspiration or core-needle biopsy. Surgical excision of lymph nodes is not
             permitted.

          -  Patients with multifocal tumors are eligible provided at least one focus is sampled
             and centrally confirmed as HER2-positive.

          -  Patients with multicentric tumors are eligible provided all discrete lesions are
             sampled and centrally confirmed as HER2-positive.

          -  Eastern Cooperative Oncology Group Performance Status of 0 or 1

          -  Baseline LVEF >= 55% measured by echocardiogram (ECHO) or multiple-gated acquisition
             (MUGA) scans

          -  Adequate hematologic and end-organ function obtained within 14 days prior to
             initiation of study treatment

          -  For women of childbearing potential: agreement to remain abstinent or use
             contraceptive methods, and agreement to refrain from donating eggs

          -  For men: agreement to remain abstinent or use contraceptive measures, and agreement to
             refrain from donating sperm

        Exclusion Criteria:

          -  Prior history of invasive breast cancer

          -  Stage IV (metastatic) breast cancer

          -  Patients with synchronous bilateral invasive breast cancer

          -  Prior systemic therapy for treatment of breast cancer

          -  Previous therapy with anthracyclines or taxanes for any malignancy

          -  Ulcerating or inflammatory breast cancer

          -  Undergone incisional and/or excisional biopsy of primary tumor and/or axillary lymph
             nodes

          -  Sentinel lymph node procedure or axillary lymph node dissection prior to initiation of
             neoadjuvant therapy

          -  History of other malignancy within 5 years prior to screening, with the exception of
             those patients who have a negligible risk of metastasis or death

          -  Cardiopulmonary dysfunction

          -  Dyspnea at rest

          -  Active or history of autoimmune disease or immune deficiency

          -  Pregnancy or breastfeeding, or intention of becoming pregnant during study treatment
             or within 5 months after the final dose of atezolizumab/placebo, 6 months after the
             final dose of doxorubicin, 12 months after the final dose of cyclophosphamide, 6
             months after the final dose of paclitaxel, or 7 months after the final dose of
             trastuzumab, pertuzumab, or trastuzumab emtansine whichever occurs last

        Exclusion Criteria Related to Trastuzumab Emtansine in the Adjuvant Setting:

          -  Patients who achieved pCR

          -  Evidence of clinically evident gross residual or recurrent disease following
             neoadjuvant therapy and surgery

          -  Unable to complete surgery with curative intent after conclusion of neoadjuvant
             systemic therapy

          -  Patient discontinued treatment with trastuzumab because of toxicity during the
             neoadjuvant phase of the study

          -  Clinically significant history of liver disease, including cirrhosis, current alcohol
             abuse, autoimmune hepatic disorders, or sclerosis cholangitis

          -  Patients with Grade >=2 peripheral neuropathy

          -  Prior treatment with trastuzumab emtansine