What Is Targeted Therapy for Cancer?

Targeted cancer therapies block specific proteins or genes that help cancers grow and spread. For some types of cancer, they may work better than other treatments like chemotherapy.

The FDA has approved targeted therapies for more than 15 types of cancer, including those of the breast, prostate, colon, and lung. But they only work if your tumor has the right target. And targeted therapies can often stop working if the target changes or your cancer finds a way around the treatment.

Researchers are learning more about the changes that drive cancer. This could lead to better targeted therapies in the future.

Types of Targeted Therapies

There are two main types of targeted therapies: small molecule medicines and monoclonal antibodies.

Small molecule medicines are small enough to slip inside cancer cells and destroy them.

You can often spot small molecule meds because their generic name ends in "-ib." For example, imatinib (Gleevec) treats chronic myelogenous leukemia (CML) and other cancers by blocking signals that tell tumor cells to grow.

Monoclonal antibodies are too big to get into cells. Instead, they attack targets on the outside of cells or right around them. Sometimes they're used to launch chemo and radiation straight into tumors. You usually get them through an IV in a vein in your arm at a hospital or clinic. Sometimes they're given as a shot.

The generic names of monoclonal antibodies end in "-mab." Bevacizumab (Avastin) is a monoclonal antibody that works by blocking blood vessels that feed tumors.

Scientists have come up with many small molecule meds and monoclonal antibodies that make use of different targets to treat cancer in different ways.

Hormone therapies stop your body from making the hormones some breast and prostate cancers need to grow, or they keep the hormones from working.

Breast cancer medicines like tamoxifen block the female hormone estrogen. Aromatase inhibitors lower the amount of estrogen in your body. For prostate cancer, doctors may prescribe meds that block male sex hormones or stop your body from making them.

Signal transduction inhibitors are the most common targeted therapies. They block signals that tell cells to divide too much and too fast.

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One example is the breast cancer medication trastuzumab (Herceptin). A protein on the outside of cells called HER2 receptor picks up signals telling the cell to grow and divide. HER2-positive breast cancers make too much of this protein, so the cancer keeps getting told "Grow! Grow! Grow!" Trastuzumab can slow or stop this type of breast cancer by latching onto HER2 receptor proteins, like putting tinfoil over the windows.

Gene expression modulators. This type of targeted therapy works to change the proteins that control the way the instructions of genes in cancer cells get carried out, or are expressed, because it's abnormal.

Apoptosis inducers. Cancer cells often find a way around the natural process of apoptosis, where healthy cells die when they're old or damaged. Apoptosis inducers cause cancer cells to go through normal cell death.

Bortezomib (Velcade) is a drug that does this to lymphoma and multiple myeloma, a blood cancer. Scientists are also studying plant compounds like resveratrol (found in red wine) to see if they might trigger cancer cell death.

Angiogenesis inhibitors block the growth of blood vessels that cancer cells form to get their nutrients and oxygen. Some target a substance called vascular endothelial growth factor (VEGF). Others go after different substances that trigger blood vessel growth. If a tumor already has a blood supply, targeted therapies can get rid of it.

Immunotherapies use your immune system to destroy cancer cells. Some boost your immune system so it does a better job of hunting down cancer. Others mark tumor cells so it's easier for your immune system to find them.

Who Gets Targeted Therapy

Some types of cancer, like CML, almost always have a target that treatment can focus on. But sometimes, your doctor will need to test your tumor to see if it has any targets. Sometimes they'll do a biopsy -- take a small sample from the tumor and check it in a lab.

Even if you have the same type of cancer as someone else, you might not have the same target. Not all breast cancers are HER2-positive. Targeted colon cancer medicines like cetuximab (Erbitux) won't work if you have the KRAS gene mutation.

Before your doctor recommends a targeted therapy, you might have to try other treatments first.

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Side Effects

Targeted therapies can cause serious side effects. Common ones are diarrhea, liver problems like hepatitis, and changes to your skin, hair, and nails.

Skin problems are the toughest for most people to deal with. They happen because targeted cancer therapies attack the same growth factors and blood vessels you need for healthy skin. Watch for:

  • A rash that looks like acne on your scalp, face, neck, chest, and back. It may itch, burn, sting, or hurt. Sometimes it can get infected. It usually lasts the whole time you're treated but goes away after treatment stops.
  • Feeling like you have a bad sunburn. This may start even before you see any changes in your skin.
  • Extreme sensitivity to sunlight.
  • Dry skin. Nearly everyone on targeted therapy has it. Your skin may crack open, especially on your hands and feet, making it hard to use your hands or walk.
  • Swollen, painful sores on your fingernails and toenails.
  • Sores on your scalp and hair loss or baldness. Your hair may turn an odd color or not grow back after treatment.
  • Your eyelids may be red, swollen, and turn inward or downward. This could damage the clear layer on the front of your eye called the cornea.

Before you start treatment, switch to gentle, chemical- and fragrance-free soaps and shampoos. Tell your doctor about any skin changes right away. You need to treat them so you don't get an infection. If skin changes are severe, you may need to stop targeted medications.

Targeted therapies can cause other side effects. Some are life-threatening.

Many targeted therapies work better combined with other treatments like chemo and radiation, so you could be dealing with those side effects as well.

Your doctor can explain what to expect from your treatment plan.

Cost

Targeted therapies can cost tens of thousands of dollars a month. One type of immunotherapy, called CAR T, can be close to half a million dollars.

Still, the price can vary depending on the type of medication, how it's given, where you get it, and how long you take it. For instance, you'll likely pay more out-of-pocket for pills than for treatment you get by IV in a hospital or clinic.

Before you start any kind of cancer treatment, be sure to find out what your insurance will pay for.

WebMD Medical Reference Reviewed by Laura J. Martin, MD on February 20, 2019

Sources

SOURCES:

Cancer.Net: "Understanding Targeted Therapy."

American Cancer Society: "Chemotherapy for Chronic Myeloid Leukemia," "Side Effects of Targeted Cancer Therapy Drugs," "Things to Know Before Getting Targeted Cancer Therapy."

National Cancer Institute: "Targeted Cancer Therapies," "How Imatinib Transformed Leukemia Treatment and Cancer Research," "Hormone Therapy for Prostate Cancer," "Targeted Therapy to Treat Cancer."

World Cancer Research Journal: "Overview of FDA-Approved Anti Cancer Drugs Used for Targeted Therapy."

Cancer Research UK: "Imatinib (Glivec)," "Cetuximab (Erbitux)."

Susan G. Komen: "Hormone Therapies."

Breastcancer.org: "How Herceptin Works."

Proceedings of the National Academy of Sciences of the United States of America: "Tumor-suppressive miR-34a induces senescence-like growth arrest through modulation of the E2F pathway in human colon cancer cells."

Oncotarget: "Apoptosis inducers in chronic lymphocytic leukemia."

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