Trastuzumab deruxtecan for unresectable or metastatic HER2-low (HR+/-) breast cancer – after chemotherapy

Trastuzumab deruxtecan is in clinical development for the treatment of adults with HER2-low, hormone receptor (HR) positive or HR negative (HR+/-), unresectable and/or metastatic breast cancer (BC) who have previously been treated with chemotherapy. Metastatic BC (stage IV) is when the cancer has spread beyond the breast and nearby lymph nodes, whilst unresectable refers to cancer that cannot be treated by surgery. HER2 receptors help control how a healthy breast cell grows, divides, and repairs itself. In the case of IHC 0 and 1+ results or IHC+ with a negative ISH assay, BC is considered HER2-low (or HER2-negative). Breast tumours are tested for both oestrogen receptors (ER) and progesterone receptors (PR). About 74 % of all BCs are both HR-positive (HR+) and HER2-negative. In England, adults with stage 4 breast cancer, that were diagnosed between 2012-2016 and followed up to 2017, had a 66% survival rate one year after diagnosis.