The introduction of new biological agents into the clinic has had a major impact on breast cancer care. Of all well-studied biological agents, Trastuzumab is the only one that has become part of the standard therapy for advanced as well as for early breast cancer. Dr. Tahover and her colleagues' review in this issue of "Harefuah" presents the pivotal trials that have brought a change of practice in the adjuvant treatment of patients with breast cancer and HER2 positive tumors. More than 10,000 patients with tumors that were defined as human epidermal growth factor receptor 2, ErbB-2 positive have been recruited into these trials. Trastuzumab was given concomitantly with or sequentially after chemotherapy. The review teaches us that despite this large cohort, several crucial issues need further clarification: Exactly who are the candidates for this specific treatment? What is the preferred protocol for the combination of Trastuzumab and chemotherapy? What is the optimal duration of treatment with Trastuzumab in the adjuvant setting? In this editorial we discuss these topics based on published data from prospective and retrospective studies.