In HER2-low disease, T-DXd is currently approved for patients who have received at least one prior line of chemotherapy and studies such as DESTINY-Breast 06 (NCT0449425) are assessing if this medication could move to the first line setting, once endocrine therapies are exhausted in HR-positive, HER2-low advanced breast cancer. This evidence concerns the gene ERBB2 and breast cancer.