Trastuzumab deruxtecan for treating HER2-low, HR-positive, metastatic breast cancer

Trastuzumab deruxtecan is in clinical development for the treatment of human epidermal growth factor receptor (HER)2-low, hormone receptor positive (HR+), advanced or metastatic breast cancer in people whose disease has progressed after previous endocrine therapy. Breast cancer occurs when abnormal cells in the breast begin to grow and divide in an uncontrolled way and eventually form a growth (tumour). Cancers that have receptors for the hormones oestrogen or progesterone are HR+, and HER2-low tumours are those whose cells contain lower levels of the HER2 protein on their surface. Metastatic cancers have spread from where they started to other parts of the body. Currently available HER2-directed therapies have been ineffective in people with HER2-low cancers. There are no therapies available in the UK specifically for HER2-low breast cancer.