What is targeted therapy for cancer?
Targeted therapy is a form of cancer treatment. It consists of special types of drugs that interact and interfere with molecular targets—typically proteins—that cancer cells possess themselves or that the cancerous tumor needs to grow and spread. Targeted therapy for breast cancer, lung cancer, kidney cancer, brain cancer, ovarian cancer, prostate cancer, gastrointestinal cancer, melanoma, and blood cancer is becoming a standard part of treatment.
Targeting cancer cells and how they grow is different from standard chemotherapy—or chemo. Chemo works by killing rapidly dividing cells. This includes cancer cells and some normal cells, such as hair follicles and the lining of the digestive tract. Because of this, chemo is toxic to some normal cells inside the body and causes problematic side effects for people taking chemotherapy drugs, such as hair loss and diarrhea.
Targeted cancer therapy can also cause side effects because the drugs may interfere with the same chemical signals found in healthy cells. Fortunately, targeted therapy usually does not cause the same intensity of side effects as standard chemo. Because of this, people often tolerate targeted therapy cancer drugs better. When side effects of targeted drugs are severe, the prescribing doctor can adjust the dose or may be able to substitute a different targeted therapy.
The two main types of targeted therapies include monoclonal antibodies and what’s known as small molecules:
Monoclonal antibodies are proteins themselves and use targets on the surface of cancer cells. They specifically recognize and attach, or bind to these targets and interfere with the ability of the cancer cells to grow. Scientists have also developed versions that can carry toxic substances directly to the cancer cell using these surface targets. Growth factors outside the cancer cell can also be targets for monoclonal antibodies. These drug names end with –mab, for monoclonal antibody. Cancer treatment guidelines may classify them as immunotherapy.
Small molecules can get inside cells. Small molecule-type targeted therapies can work both on cancer cells and cells that perform functions the cancer cell needs to grow and spread. The targets inside the cells are often enzymes. Interfering with or inhibiting enzymes stops various cellular functions. These drug names end with –ib, for inhibit.
Hormone therapy can also be a form of targeted therapy. However, cancer treatment guidelines usually list hormone therapies separately. Some cancers rely on hormones to grow. The hormones attach to receptors (another type of protein) on the cancer cells. There are drugs that can block these receptors. This keeps the cancer cell from being able to use the hormone to grow. There are also drugs that lower natural levels of hormones to starve the cancer of the fuel it needs. Hormone therapy is a common targeted therapy for hormone-receptor positive breast cancer.
Why is targeted therapy prescribed?
Not all cancers will respond to targeted therapy. During diagnosis, test results will tell your doctor whether the cancer is likely to respond to targeted therapy. There are several kinds of tests that look for specific markers, gene mutations, and other tumor characteristics. Targeted therapy may be an option when any of these features are present.
Doctors commonly use targeted therapy for the following cancers:
Who prescribes targeted therapy?
Your oncologist will prescribe targeted therapy using diagnostic test results. Oncologists specialize in diagnosing, treating and preventing cancer.
How is targeted therapy given?
How you receive targeted therapy depends on the type. Small molecules are tablets or capsules you can take at home. Monoclonal antibodies are IV (intravenous) medicines. You will go to your doctor’s office, clinic, or outpatient unit in a hospital to receive these drugs. Hormones can be either oral medicines or shots.
How often and the length of time you take the medicine depends on the specific drug, the type and stage of cancer, and how you respond to the drug. It could be daily, weekly or monthly. Similar to chemotherapy or radiation therapy, you may receive treatment in cycles to give your body time to rest and recover.
What are the side effects of targeted therapy?
Targeted therapy does not cause the same intensity of side effects as standard chemo. But there are still some potentially serious problems with targeted therapy including:
Blood clotting and wound healing problems
Brain and nervous system damage
Vision problems, such as dry eye, keratitis, and vascular leakage, which is when plasma and other components leak from blood vessels
Some of these side effects actually indicate an enhanced response to the drug. For some drugs, people who develop certain side effects tend to have better outcomes than those who do not. If you notice any new symptoms or side effects, make sure your doctor knows. Even if they are good signs, your doctor may need to treat them.
How do I prepare for targeted therapy?
You can prepare for targeted therapy by finding out what to expect and how, if necessary, to alter your diet and activity during treatment.
Questions to ask your doctor
Here are some questions you may want to ask your doctor about targeted therapy:
How and when will I take targeted therapy?
What should I do if I miss a dose?
What kind of monitoring or testing will I need during treatment?
Are there vitamins or herbal supplements I should take or avoid during treatment?
Can I drink alcohol and caffeine during treatment?
What are the possible side effects and drug interactions? How can I prevent or manage them?
Are there any symptoms or side effects that should prompt me to call you or seek medical care?
Are there any restrictions on my activities during treatment?
What can I expect from targeted therapy?
Although targeted therapy first became a reality for some cancer patients in the early 2000’s, it is still considered a breakthrough in cancer treatment. This is especially true for targeted therapy for lung cancer. However, it does not always work. Some tumors do not respond well despite having the molecular target. And sometimes, the drug works, but loses its effectiveness with time. This happens because it is possible for the cancer cells to become resistant to the drug. Resistance can occur through mutations or changes in the target. The targeted therapy can no longer interact with the target because it is now “looks” different. Resistance can also happen when the tumor finds a way to grow that doesn’t depend on the targeted pathway.
To fight drug resistance, doctors typically use a combination of drugs. This may be two targeted therapies or a targeted therapy with standard chemo. Research suggests this approach can be successful.
Your doctor will monitor you closely during treatment. You will have exams and follow-up testing to measure whether the drug is working. Talk with your doctor before starting treatment to understand the risks and benefits. Keep the conversation going during treatment so you know how it is progressing.