Use of subcutaneous and intravenous trastuzumab: real-world experience from three hospitals in Sweden.

We aimed to describe the use of subcutaneous (sc.) trastuzumab use in a real-world setting. This retrospective cohort study evaluated electronic medical records of patients with early breast cancer and trastuzumab use from January 2010 to February 2018 in three hospitals in Sweden. In total, 363 patients received trastuzumab during study period. Of these, 217 (59.8%) patients started treatment with sc. trastuzumab and 146 (40.2%) with intravenous trastuzumab. After sc. trastuzumab approval, use of sc. trastuzumab increased from 70.2% in 2014 to 100% in 2017. Since 2013, 34 of 35 (97.4%) patients who started with intravenous trastuzumab switched to sc. formulation. Trastuzumab sc. quickly became the prevailing formulation for treatment in HER2-positive early breast cancer.