This multicenter study in participants with HER2-positive eBC will investigate participants' pain and discomfort of SC trastuzumab (Herceptin) administered either via a single-use injection device (SID) or via vial for manual administration using a hand-held syringe (SC vial). In total, participants will obtain at least 18 cycles/1 year of trastuzumab (4 cycles of intravenous [IV] and 14 cycles of SC trastuzumab).

Inclusion Criteria:

• Eastern Cooperative Oncology Group (ECOG) performance status 0 or 1
• Hormonal therapy allowed as per institutional guidelines
• Left ventricular ejection fraction (LVEF) of greater than or equal to (>/=) 55 percent (%) measured by echocardiography (ECHO) prior to first dose of trastuzumab
• HER2-positive disease immunohistochemistry (IHC) 3+ or in-situ hybridization (ISH) positive as determined in a local laboratory that is experienced/certified in HER2-expression testing using an accurate and validated assay
• Histologically confirmed non-metastatic primary invasive adenocarcinoma of the breast
• No evidence of residual, locally recurrent or metastatic disease after completion of surgery and chemotherapy, or during concurrent chemotherapy (neo-adjuvant or adjuvant)
• Participants who have completed all (neo)adjuvant treatment or participants after adjuvant chemotherapy with doxorubicin and cyclophosphamide (AC) to whom the 4 subsequent cycles of trastuzumab in combination with paclitaxel or docetaxel are indicated per local practice
• Not more than 3 months should have elapsed since the last dose of adjuvant chemotherapy in case of subsequent treatment scheme

Exclusion Criteria:

• Previous neoadjuvant or adjuvant breast cancer treatment with an approved or investigational anti-HER2 agent
• History of other malignancy that can affect compliance with the protocol or interpretation of results. Participants with curatively treated carcinoma in situ of the cervix or basal cell carcinoma, and participants with other curatively treated malignancies who have been disease-free for at least 5 years, are eligible. Participants with previous ductal carcinoma in situ (DCIS) of the breast are also eligible for the study
• 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
• Prior maximum cumulative dose of doxorubicin >360 mg/m2 or maximum cumulative dose of epirubicin >720 mg/m2 or equivalent
• 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
• Concurrent enrollment in another clinical trial using an investigational anticancer 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®, 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
• Major surgical procedure or significant traumatic injury within 14 days prior to the first dose of study treatment or anticipated need for major surgery during the course of study treatment