Targeted Cancer Therapies

Posted: March 1, 2005

Targeted cancer therapies use drugs that block the growth and spread of cancer by interfering with specific molecules involved in carcinogenesis (the process by which normal cells become cancer cells) and tumor growth.

Because scientists call these molecules “molecular targets,” therapies that interfere with them are sometimes called “molecular-targeted drugs,” “molecularly targeted therapies,” or other similar names.

By focusing on molecular and cellular changes that are specific to cancer, targeted cancer therapies may be more effective than current treatments and less harmful to normal cells.

Most targeted cancer therapies are in pre-clinical testing (research with animals), but some are in clinical trials (research studies with people), or have been approved by the U.S. Food and Drug Administration (FDA). Targeted cancer therapies are being studied for use alone, in combination with each other, and in combination with other cancer treatments, such as chemotherapy.

What are some of the cellular changes that lead to cancer?
Normally, cells grow and divide to form new cells as the body needs them. When cells grow old, they die, and new cells take their place. Sometimes this orderly process goes wrong. New cells form when the body does not need them, and old cells do not die when they should. These extra cells can form a mass of tissue called a growth or tumor.

The cells in malignant (cancerous) tumors are abnormal and divide without control or order. They can invade and damage nearby tissues and organs. Also, cancer cells can break away from a malignant tumor and spread to other parts of the body.

Normal cell growth and division are largely under the control of a network of chemical and molecular signals that give instructions to cells. Genetic changes can disrupt the signaling process so that cells no longer grow and divide normally, or no longer die when they should.

Alterations in two types of genes can contribute to the cancer process. Proto-oncogenes are normal genes that are involved in cell growth and division. Changes in these genes lead to the development of oncogenes, which can promote or allow excessive and continuous cell growth and division. Tumor suppressor genes are normal genes that slow down cell growth and division. When a tumor suppressor gene does not work properly, cells may be unable to stop growing and dividing, which leads to tumor growth.

To use the metaphor of a car, the presence of an oncogene is like having a gas pedal that is stuck to the floorboard, causing cells to continually grow and divide. Tumor suppressor genes act like a brake pedal. The loss of a functioning tumor suppressor gene is like having a brake pedal that does not work properly, allowing cells to continually grow and divide.

Abnormal proteins
Genetic changes that are not corrected by the cell can lead to the production of abnormal proteins. Normally, proteins interact with each other as a kind of relay team to carry out the work of the cell. Damaged proteins may not respond to normal signals, may over-respond to normal signals, or otherwise fail to carry out their normal functions. Cancer develops when abnormal proteins inside a cell cause it to reproduce excessively and allow that cell to live longer than normal cells.

How do targeted cancer therapies work?
Targeted cancer therapies interfere with cancer cell growth and division in different ways and at various points during the development, growth and spread of cancer. Many of these therapies focus on proteins that are involved in the signaling process. By blocking the signals that tell cancer cells to grow and divide uncontrollably, targeted cancer therapies can help to stop the growth and division of cancer cells.

What impact will targeted therapies have on cancer treatment?
Targeted cancer therapies will give doctors a better way to tailor cancer treatment. Eventually, treatments may be individualized based on the unique set of molecular targets produced by the patient’s tumor. Targeted cancer therapies also hold the promise of being more selective, thus harming fewer normal cells, reducing side effects and improving the quality of life.

Source: National Cancer Institute (NCI) Resources

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