Trastuzumab Deruxtecan (T-DXd) is a medication used in this clinical trial to treat breast cancer. It is specifically designed for patients with HER2-low, hormone receptor-positive breast cancer that has progressed despite previous endocrine therapy. This medication works by targeting and delivering chemotherapy directly to cancer cells, which may help to slow down or stop the growth of the cancer.

Investigator’s Choice Chemotherapy refers to a selection of standard chemotherapy treatments chosen by the doctors involved in the trial. These treatments are used as a comparison to evaluate the effectiveness of Trastuzumab Deruxtecan. The specific chemotherapy drugs used can vary, but they are commonly used options for treating breast cancer that has not responded to other treatments.

HER2-Low, Hormone Receptor Positive Breast Cancer – This type of breast cancer is characterized by low levels of the HER2 protein and the presence of hormone receptors. It typically occurs when cancer cells have a HER2 protein expression that is lower than what is considered HER2-positive but higher than HER2-negative. The cancer progresses as it grows and spreads to other parts of the body, often after initial treatment with hormone therapy. This progression can lead to the cancer becoming more aggressive and resistant to standard treatments. The disease is often monitored for changes in tumor size and spread to assess its progression. Understanding the specific characteristics of this cancer type is crucial for determining the most effective treatment approach.