Targeted therapy is a type of cancer treatment that uses drugs to target specific genes and proteins that help cancer cells survive and grow. It is a foundation of precision medicine, which is based on identifying the specific genetic changes that help a tumor grow and change. An ideal target for this kind of therapy would be a protein that is present in cancer cells but not healthy cells. Targeted therapy can affect the tissue environment that cancer cells grow in or it can target cells related to cancer growth, like blood vessel cells. Most targeted therapies are either small-molecule drugs or monoclonal antibodies. Small-molecule drugs are small enough to enter cells easily, so they are used for targets that are inside cells. Targeted therapy can treat many different types of cancer and can also be used in combination with other cancer treatments, such as chemotherapy. However, not all cancers have targeted therapies available yet, and most people getting targeted therapy also need surgery, chemotherapy, radiation therapy, or hormone therapy. Targeted therapy helps treat cancer by interfering with specific proteins that help tumors grow and spread throughout the body, which is different from chemotherapy that often kills all cells that grow and divide quickly.