All About Targeted Therapy

What is targeted therapy?

Targeted therapy is a type of cancer treatment. Targeted therapies use drugs to target genes and proteins that control how cancer cells grow, divide, and spread. This slows down or kills the cancer cells while avoiding harm to normal cells as much as possible. Sometimes the “target” is found on some healthy cells, and side effects can happen.

Targeted therapy is also called precision medicine or personalized medicine. This is because one person’s cancer may be treated differently than another person's based on the targets found on their tumor. Your healthcare provider will have to test your tumor to see which target is there. Targeted therapy often works, but it does not always work. Here are some examples:

• The same type of cancer does not always have the same molecular targets that match the treatment.
• The same targeted treatment doesn’t work for everyone with the same type of cancer. Some tumors react to the therapy differently.
• Even if a certain target is there, it does not mean the tumor will respond to the targeted therapy.

Common molecular targets (mutations or changes) treated with targeted therapies are HER2, EGFR, KRAS, VEGF, ALK, JAK 1 and 2, BTK, and BRAF. Your healthcare team may test for these mutations, based on your cancer type and if a mutation is known in that cancer type.

Targeted therapies are FDA-approved for the treatment of many cancers. Targeted therapy may be given by itself or with chemotherapy, radiation, and/or surgery.

What are the types of targeted therapies?

There are different types of targeted therapy, and each type works a little differently. Some targeted therapies work by focusing on the inside of the cancer cell while others focus on the outside of the cancer cell. The two most common types of targeted therapy are:

• Small-molecule medications: These focus on the inside of the cancer because of their small size. They find the target, enter the cell, and block the target so it dies.
• Large-molecule medications: These often don’t fit into a cell because of their large size. They focus on the outside of the cancer cell by attacking the proteins or enzymes on the surface of the cell so that it dies.

Examples of targeted therapies are:

• Kinase Inhibitors: Cell growth is controlled by growth factors. They attach to the surface of cells triggering a series of chemical reactions that let the cell grow and divide. Cancer cells do not work properly and can grow and divide even when growth factors are not present. Kinase inhibitors work by blocking signals within cancer cells, stopping a step needed for the cell to grow and divide. Examples of kinase inhibitors are dabrafenib (Tafinlar®), imatinib (Gleevec®), sorafenib (Nexavar®), ibrutinib (Imbruvica), and cabozantinib (Cometriq).
• Angiogenesis Inhibitors: Angiogenesis is the making of blood vessels that give the tumor the nutrients it needs to grow. These medications work by stopping this blood supply from being made and cutting off the tumor's source of nutrients. Some kinase inhibitors also act as angiogenesis inhibitors (Examples: sorafenib (Nexavar), sunitinib (Sutent®), everolimus (Afinitor®). Examples of angiogenesis inhibitors are ziv-aflibercept (Zaltrap®), lenalidomide (Revlimid®), and vandetanib (Caprelsa®).
• Monoclonal antibodies: These antibodies are made in a lab and target a specific antigen (protein). They work in a few different ways. They can target a specific cell (the cancer cell), sending a message to the immune system to destroy the targeted cell. Some monoclonal antibodies slow or stop the growth of cancer cells by getting in the way of functions necessary for cell growth. Examples of monoclonal antibodies are bevacizumab (Avastin®), trastuzumab (Herceptin®), and denosumab (Xgeva®, Prolia®).
• Radioimmunotherapy: This is a combination of a monoclonal antibody and a radiation source, so radiation can be delivered right to the targeted cells, but often in lower doses and over a longer amount of time. An example is ibritumomab tiuxetan (Zevalin®).

How are targeted therapies given?

Some targeted therapies are given as a pill, others are given through a vein (IV). Be sure to store and handle oral medications as you are told to by your care team. It is important that you take your oral medications exactly as your provider tells you to.

Some oral medications are very expensive. Talk with your care team if you can’t afford your medication, help may be available.

What are the side effects of targeted therapies?

There are side effects of targeted therapies. Not everyone will have the same side effects. Talk with your healthcare provider about which side effects you may have.

Side effects are different for each drug depending on how your body reacts to it. Some side effects are:

• Skin problems, including dry skin or rash.
• Diarrhea.
• Liver problems.
• Heart problems.
• High blood pressure.
• Problems with wound healing and blood clotting.
• Nail changes.
• Loss of hair color.
• Gastrointestinal (GI) perforation.

Do not stop taking your oral medications if you have side effects. If you are having side effects talk with your healthcare provider, there are medications that can help. Most short-term side effects will go away over time once you are done with treatment.

Because many of these drugs are newer, we don’t know a lot about possible long-term side effects. Be sure to talk with your healthcare team about fertility before starting any targeted therapy, as these medications may impact your ability to have a child. Certain targeted therapies like thalidomide and lenalidomide can cause serious birth defects and have special programs in place to educate patients of childbearing age.

How will I know if targeted therapy is working for me?

Over time, your cancer may stop responding to the targeted medication you are taking. This happens more often when targeted therapy is the only therapy being used. Your healthcare team will monitor your disease closely throughout your treatment. You will have regular blood and imaging (CT scan, PET scan) tests that will tell how your body is responding to treatment.

Resources for More Information

• American Cancer Society: Targeted Therapy. 
• National Cancer Institute: Targeted Therapy to Treat Cancer. 
• National Cancer Institute: List of Targeted Therapy Drugs Approved for Specific Types of Cancer.