Tumors in about 15% of patients with breast cancer overexpress HER2. Trastuzumab (Herceptin®; F. Hoffmann–La Roche, Basel, Switzerland) is a humanized monoclonal antibody against HER2. While the introduction of trastuzumab has changed the natural course of HER2-positive breast cancer, the need for repeated administration of the drug over a prolonged period of time represents a challenge. Similarly to other chronic disorders, subcutaneous administration of monoclonal antibodies may be of advantage in this setting. The results of a prospective randomized Phase III study have demonstrated that subcutaneous trastuzumab is noninferior compared with the intravenous administration of the drug in terms of efficacy (assessed as pathological complete response rate) as well as in pharmacokinetic parameters. Moreover, another prospective randomized study showed that an overwhelming majority of patients prefer subcutaneous over intravenous trastuzumab. The advent of subcutaneous trastuzumab represents an important progress in the concept of cancer management that is based also on patient choice and preferences.