This study is a randomized Trastuzumab-controlled double-blind parallel-group study.

Inclusion Criteria:

1. Healthy Japanese male adults
2. Body Mass Index (BMI) between 17.6 and 26.4 kg/m² at the time of screening BMI = Body Weight (kg)/[Height (m)]²
3. The individual who freely consents to participate after receiving a detailed explanation of the clinical study and completely understanding thereof, and who has capacity to follow precautions and provide written consent.

Exclusion Criteria:

1. History of hypersensitivity to components of Trastuzumab or diphenhydramine or any other drug
2. Use of any ethical drug within 2 weeks before investigational product administration or any over-the-counter drug within 1 week before investigational product administration that would affect study participation in the opinion of the investigator or subinvestigators (except for diphenhydramine, which will be used concomitantly in the present clinical trial and any drug applied locally and having no systemic actions)
3. History of allergic symptoms such as bronchial asthma and urticaria that would affect study participation in the opinion of the investigator or subinvestigators
4. History of cardiac disorders, hypertension, coronary artery disease (e.g., myocardial infarction, angina), and/or vascular disorder; ongoing palpitations, shortness of breath, and/or tachycardia