According to the results of the conducted studies in the early 2000’s, adjuvant trastuzumab for 1 year has been admitted the gold standard since 2006. However, the high cost of treatment and the increasing of the risk of cardiotoxicity have led to new clinical trials concerning the short-course trastuzumab regimen. The study deals with the results of the number of the largest randomized trials associated with the comparison of 6 months (the PHARE trial and the HORG study), 9 weeks (the Short-HER study and the SOLD study) and 12 months duration of adjuvant trastuzumab therapy in combination with chemotherapy in patients with HER2-possitive early breast cancer. Today, none of the studies has shown statistically significant evidence of the possibility to reduce the duration of adjuvant trastuzumab therapy.