Trastuzumab represented a breakthrough in the treatment of patients with HER2-positive breast cancer. Numerous clinical trials have shown its efficacy in patients with early, locally advanced and metastatic breast cancer. A more convenient formulation of subcutaneous (s.c.) trastuzumab has been developed. Based on the HannaH trial, which compared s.c. trastuzumab with the intravenous (i.v.) formulation, the European Medicines Agency has registered s.c. trastuzumab. The study showed that pathologic complete response and serum trough concentration at predose cycle 8, were non-interior to i.v. administration. Recently, the results of the HannaH study were presented with a median follow-up of 40 months. Event-free survival (no recurrence, progression or death due to any cause) rates at 3 years were similar in two arms (76% in trastuzumab s.c. and 73% in trastuzumab i.v. arm). In the PrefHer study most patients, as well as health-care professionals, preferred trastuzumab s.c. Injection-site reactions were mild and observed only in patients with trastuzumab s.c. Large SafeHer trial evaluating safety and tolerability of this drug formulation is ongoing. Preliminary results confirm the previous reports and safety of this therapy. Additionally, s.c. administration of trastuzumab reduces time of injection, patient time in care unit, risk of errors in drug dosage (fixed dose) and allows the performance of other duties within existing health-care resources.