This Phase IIIb, open-label, multinational, multicenter study will evaluate the participant's satisfaction and safety with subcutaneously administered trastuzumab in participants with HER2-positive early breast cancer. Participants will receive trastuzumab 600 milligrams (mg) administered subcutaneously every 3 weeks in the adjuvant or neo-adjuvant plus adjuvant setting for 18 cycles (1 year), unless disease progression or unacceptable toxicity occurs. The trastuzumab regimen could include mono- and/or combination therapy.

Inclusion Criteria:

• Eastern Cooperative Oncology Group (ECOG) performance status 0-1
• Hormonal therapy will be allowed as per institutional guidelines
• Prior use of anti-HER2 therapy will be allowed, except for early breast cancer participants in the neo-adjuvant setting
• Left ventricular ejection fraction (LVEF) of greater than or equal to (>=) 55 percent (%) measured by echocardiography (ECHO) or multiple gated acquisition (MUGA) scan prior to first dose of trastuzumab, 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
• HER2-positive disease immunohistochemistry 3 plus (IHC3+) 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)
• 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 participants with other curatively treated malignancies who have been disease-free for at least 5 years, are eligible
• Severe dyspnea at rest or requirement for supplementary oxygen therapy
• 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
• 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, or a history of severe allergic or immunological reactions, e.g. difficult to control asthma
• Inadequate bone marrow, hepatic or renal function