Trastuzumab deruxtecan is a medication used in this clinical trial to treat advanced breast cancer. It is designed to target and attach to specific proteins on cancer cells, helping to deliver a powerful anti-cancer drug directly to the tumor. This targeted approach aims to kill cancer cells more effectively while minimizing damage to healthy cells.

CDK4/6 inhibitor-based endocrine therapy is another treatment option being studied in this trial. This therapy combines a type of medication known as a CDK4/6 inhibitor with hormone therapy. CDK4/6 inhibitors work by blocking certain proteins that cancer cells need to grow and divide. When used with hormone therapy, which targets hormone receptors on cancer cells, this combination aims to slow down or stop the growth of cancer cells in patients with hormone receptor-positive breast cancer.

Unresectable Locally Recurrent or Metastatic Hormone Receptor-Positive and Human Epidermal Growth Factor Receptor 2-Low/Ultralow Breast Cancer – This type of breast cancer is characterized by its inability to be surgically removed and its recurrence in the local area or spread to other parts of the body. It is hormone receptor-positive, meaning the cancer cells grow in response to hormones like estrogen or progesterone. The cancer is also classified as HER2-low or ultralow, indicating low levels of the HER2 protein, which can affect the growth of cancer cells. The progression of this disease involves the continued growth and spread of cancer cells, which can invade nearby tissues or metastasize to distant organs. The classification as non-luminal by gene expression profiling suggests a specific pattern of gene activity that influences the cancer’s behavior. This type of breast cancer can be challenging to manage due to its advanced stage and specific biological characteristics.