The Efficacy and Safety of Trastuzumab in the Metastatic Breast Cancer.

The aim of this study was to explore the efficacy and safety of Trastuzumab-Deruxtecan (T-DXd) in metastatic breast cancer (mBC). This retrospective observational study was conducted between January 2021 and 2023. Patients' clinical and pathological characteristics and previous medicinal treatments were reviewed. The efficacy of T-DXd and its influencing factors, as well as the adverse reactions of T-DXd were also observed. The median age of the patients was 43 years, and the median number of treatment lines was 4. In the overall population, the objective response rate (ORR) was 72.7%, the disease control rate (DCR) was 90.9%, and the median progression-free survival (mPFS) was six months. Among them, two patients temporarily discontinued treatment after two cycles of T-DXd due to financial reasons, but their disease remained stable for 5 and 8 months, respectively. Efficacy was better in patients with HER-2 amplification, who had not previously used antibody drug conjugates (ADC) drugs, were sensitive to anti-HER-2 treatment, and had ≤3 lines of therapy. Common adverse reactions during T-DXd treatment included gastrointestinal reactions such as nausea, vomiting, diarrhoea, and constipation, as well as haematological toxicities, decreased appetite, hair loss, and fatigue. Some patients experienced gastritis, abnormal liver function, and weight gain, but none of the patients developed interstitial pneumonia. T-DXd can achieve significant and durable survival benefits with controllable safety in patients with HER2-positive or HER2 low-expressing mBC. Key Words: Metastatic breast cancer, Trastuzumab-Deruxtecan, Efficacy, Safety.