Traditional chemotherapy works by killing cells that multiply quickly, whether normal or cancerous. Targeted therapy, also called precision medicine, is different. It works by stopping or slowing the growth or spread of cancer.
This happens on a cellular level. Cancer cells need specific molecules (often in the form of proteins) to survive, multiply and spread. These molecules are usually made by the genes that cause cancer, as well as the cells themselves.
Targeted therapies are designed to interfere with, or target, these molecules or the cancer-causing genes that create them. In some cases, the drug will attach to the molecule it targets, stopping it from doing its job. Other times, the drug will physically block the molecule from the place it normally goes. By stopping the normal work of these molecules, cancer’s growth can be slowed or even stopped.
Because targeted therapies are made to work on specific molecules, doctors usually perform blood or DNA tests to see if and how many of these molecules are present in the patient’s body. If there are not enough, the drug will not be given. Even if a patient has enough of the targeted molecule, in some cases the drug stops working after a period of time. This usually occurs when the cancer finds some other way to finish the job the targeted therapy is made to stop.
Targeted therapies can be given in pill form or through an infusion and are often given along with another treatment like chemotherapy or radiation. There are two main types of targeted therapies drugs:
- Small molecule drugs target molecules that are inside cancer cells themselves. Because of their small size, they can easily enter the cells and interfere with the molecules inside.
- Monoclonal antibodies are larger and work outside of cancer cells. They target molecules on the surface of the cancer cells or nearby. These are made using cloned cells that produce antibodies that interfere with the targeted molecule. Monoclonal antibodies also can be used to deliver a toxic molecule directly into a cancer cell.
Side Effects of Targeted Therapies
While targeted therapies generally have fewer side effects than chemotherapy, they can still be serious. Side effects depend on the targeted therapy drug a patient is taking. Common side effects include:
- Skin problems, including hives and intense itching
- Allergic-like reactions, including trouble breathing, tightness in the chest or throat, dizziness and swelling in the lips or tongue
- Elevated liver enzymes
- Diarrhea or constipation
- Nausea and vomiting
- Low blood cell counts
- Poor blood clotting and wound healing
- High blood pressure