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Targeted therapy

Targeted therapy uses drugs to target specific molecules (for example, proteins) on the surface of or inside cancer cells. These molecules help send signals that tell cells to grow or divide. By targeting these molecules, the drugs stop the growth and spread of cancer cells while limiting harm to normal cells.

Targeted cancer therapies use different types of drugs, and each drug works differently. Researchers are studying different targeted cancer therapies in animals (preclinical testing) and in humans (clinical trials). However, few targeted therapies have been approved to treat cancer. Targeted cancer therapies may eventually prove to be more effective and less harmful than current cancer treatments.

Targeted therapy is also called molecularly targeted therapy.

How targeted therapy works

Cells send and receive chemical and molecular signals. These signals tell cells to grow, reproduce, stop reproducing or die. Usually, the signals are clear, and cells grow, divide to produce more cells and die as the body needs. Sometimes the signals get mixed up and this process is changed. Instead of dying, cells continue to grow and divide out of control. Cancer can develop when the signals cause a cell to grow and reproduce too much.

Molecular targets

Targeted therapies block the action of specific molecules involved in cancer cell growth. Some targeted therapies focus on molecules that tell cancer cells to grow and divide out of control.

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Types of targeted therapy

Different types of targeted therapies target different molecules. These molecules are usually involved in cell growth or division.

Tyrosine kinase inhibitors

Tyrosine kinases are a type of enzyme (proteins that speed up certain chemical reactions in the body). They play an important role in cell development and division. Tyrosine kinase inhibitors block specific tyrosine kinases that tell cancer cells to grow. These drugs are also called signal-transduction inhibitors or small-molecule drugs.

Examples of tyrosine kinase inhibitors include:

  • Imatinib (Gleevec) targets a tyrosine kinase that forms abnormally in chronic myelogenous leukemia (CML) and gastrointestinal stromal tumour (GIST) cells.
  • Gefitinib (Iressa) targets a tyrosine kinase in certain lung cancer cells.
  • Erlotinib (Tarceva) targets a tyrosine kinase in pancreas and lung cancer cells.

Apoptosis-inducing drugs

The natural process (a series of programmed events) that cells go through when they die is called apoptosis. In some cancer cells, the signals that tell cells to go through apoptosis don’t work properly. Apoptosis-inducing drugs help restore these signals and tell the cancer cells to die. These drugs interfere with certain proteins or enzymes involved in cell growth and survival. Apoptosis-inducing drugs can also make cancer cells more vulnerable to the effects of chemotherapy.

Examples of apoptosis-inducing drugs include:

  • Bortezomib (Velcade) is a proteosome inhibitor. It blocks a group of proteins (proteosomes) that cancer cells need to grow. Interfering with proteosomes may cause cancer cells to die and may stop cancer from growing.
  • Oblimersen (Genasense) is an antisense drug. It blocks the production of BCL2, a protein that promotes cancer cell survival and can cause resistance to anticancer drugs. Blocking BCL2 may make cancer cells more sensitive to anticancer drugs.

Biological therapies

Some biological therapies specifically interfere with cancer cell growth and don’t affect normal cell growth. These biological therapies are considered targeted therapies.

Examples of biological targeted therapies include:

  • monoclonal antibodies
    • Trastuzumab (Herceptin) is used as adjuvant therapy (given in addition to the first-line therapy) to treat HER2-positive breast cancer. It is also used to treat metastatic breast cancer.
    • Rituximab (Rituxan) is used to treat some types of non-Hodgkin lymphoma.
    • Cetuximab (Erbitux) is used to treat advanced or metastatic colorectal cancer in people with tumours that make too much (overexpress) epidermal growth factor receptor (EGFR) protein.
  • cancer vaccines
    • Bacillus Calmette-Guérin (BCG) vaccine is used to stimulate the immune system to help it recognize and destroy bladder cancer cells.
  • anti-angiogenesis drugs
    • Sunitinib (Sutent) and thalidomide (Thalomid) are examples of drugs that block the signals inside cancer cells that trigger blood vessel growth. They are used to treat a variety of cancers.
    • Bevacizumab (Avastin) is used to treat advanced or metastatic colorectal cancer.

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Getting targeted therapy

Targeted therapies may be used alone or with other types of therapy, such as chemotherapy. Targeted therapy can be given in different ways. For example, it may be given as pills or capsules that are swallowed (orally) or by needle into a vein (intravenously).

Some targeted therapy drugs must be given in the hospital. Others can be taken at home. Targeted therapy treatment is based on a set schedule, or protocol, that is based on the person’s specific condition. Each course of treatment usually involves a treatment period followed by a recovery period.

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Side effects of targeted therapy

Side effects can occur with any type of treatment, but not everyone has them or experiences them in the same way. Side effects of targeted therapy will depend mainly on the:

  • type of drug(s)
  • dose
  • person’s overall health

Side effects can happen any time during, immediately after or a few days or weeks after targeted therapy. Most side effects of targeted therapies are mild and go away once the body gets used to the drug.

It is important to report side effects to the healthcare team. Doctors may grade (measure) how severe certain side effects are. If side effects are severe, therapy may be temporarily stopped, doses may be adjusted or both.

For more detailed information on specific drugs, go to sources of drug information.

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