HER2+ breast cancer is one of the more aggressive subtypes of breast cancer, accounting for 22% of all breast cancers. However, recent advancements in targeted HER2+ therapy has significantly enhanced survival rates in those affected. Targeted therapies (i.e. Trastuzumab) utilize antibodies to specifically target and inhibit the aberrant HER2 receptors on cancer cells, decreasing their proliferation. In 2019, the KATHERINE study demonstrated that the addition of Trastuzumab emtansine (T-DM1; Brand name: Kadcyla; antibody-drug conjugate with cytotoxic activity), improved outcomes when used in adjuvant chemotherapy for HER2+ breast cancer patients who have received neoadjuvant chemotherapy with residual disease. Despite this, the study also indicated that the severe side-effects of this treatment reduced the adherence of the drug, compared to the standard therapy. Currently, there is a lack of reporting on the widespread adoption of T-DM1 in adjuvant settings and its subsequent effects. 

This retrospective chart review will evaluate patients receiving therapy for HER2+ breast cancer from January 1st, 2019 to December 31st, 2021, at the Windsor Regional Hospital (WRH). This study aims to investigate the adoption of T-DM1 in adjuvant HER2+ therapy and provide an accurate depiction of the effectiveness and compliance of undergoing this therapy in a real-life setting. Importantly, it will inform physicians about the viability of prescribing this treatment to patients.