A Study of Subcutaneous At Home Administration of Trastuzumab (Herceptin) in Participants With Human Epidermal Growth Factor Receptor 2-positive (HER2+) Early Breast Cancer (eBC)

Inclusion Criteria:

* Histologically confirmed non-metastatic primary invasive adenocarcinoma of the breast
* HER2-positive disease immunohistochemistry (IHC)3+ or in situ hybridization (ISH) positive, in line with local reimbursement criteria and determined in a local laboratory that is experienced/certified in HER2-expression testing using an accurate and validated assay
* Eastern Cooperative Oncology Group (ECOG) performance status 0-1
* Hormonal therapy will be allowed as per institutional guidelines
* Left ventricular ejection fraction (LVEF) of greater than or equal to (\>/=) 50% measured by echocardiography (ECHO) or multiple gated acquisition (MUGA) scan prior to first dose of trastuzumab SC, or, for those who were receiving trastuzumab when beginning the study, documented results within an acceptable limit from a cardiac assessment within 3 months prior to enrollment
* Participants have completed the first 6 cycles of trastuzumab IV as part of the (neo)adjuvant treatment
* No evidence of residual, locally recurrent or metastatic disease after completion of surgery and chemotherapy, (neo-adjuvant or adjuvant)
* Use of concurrent curative radiotherapy will be permitted

Exclusion Criteria:

* History of other malignancy which could affect compliance with the protocol or interpretation of results. Participants with curatively treated carcinoma in situ of the cervix or basal cell carcinoma, and patients with other curatively treated malignancies who have been disease-free for at least 5 years, are eligible
* Participants with severe dyspnea at rest or requiring supplementary oxygen therapy
* Participants with other concurrent serious diseases that may interfere with planned treatment, including severe pulmonary conditions/illness
* Serious cardiac illness or medical conditions that would preclude the use of trastuzumab, specifically: history of documented congestive heart failure (CHF), high-risk uncontrolled arrhythmias, angina pectoris requiring medication, clinically significant valvular disease, evidence of transmural infarction on electrocardiogram (ECG), diagnosed poorly controlled hypertension
* Known infection with human immunodeficiency virus (HIV), active hepatitis B virus (HBV) or hepatitis C virus (HCV)
* Pregnant or lactating women
* Women of childbearing potential and male participants with partners of childbearing potential who are unable or unwilling to use adequate contraceptive measures during study treatment
* Concurrent enrollment in another clinical trial using an investigational anti-cancer treatment, including hormonal therapy, bisphosphonate therapy and immunotherapy, within 28 days prior to the first dose of study treatment
* Known hypersensitivity to trastuzumab, murine proteins, to any of the excipients of Herceptin including hyaluronidase, or the adhesive of the SC device, or a history of severe allergic or immunological reactions, e.g. difficult to control asthma
* Inadequate bone marrow, hepatic or renal function