Biological therapy (sometimes called immunotherapy,) is a relatively new addition to the family of cancer treatments. Biological therapies use the body's immune system, either directly or indirectly, to fight cancer or to lessen the side effects that may be caused by some cancer treatments.

The immune system is a complex network of cells and organs that work together to defend the body against attacks by "foreign," or "non-self," invaders. This network is one of the body's main defenses against disease. It works against diseases such as cancer. Cancer may develop when the immune system breaks down or is not functioning adequately. Biological therapies are designed to repair, stimulate, or enhance the immune system's responses.

Immune system cells B cells, T cells, natural killer (NK) cells, and monocyte. Cells in the immune system secrete two types of proteins: antibodies and cytokines. Antibodies respond to antigens by latching onto or binding with the antigens. Specific antibodies match specific antigens, fitting together similarly the way a key fits a lock. Cytokines are substances produced by some immune system cells to communicate with other cells. Types of cytokines include lymphokines, interferon, interleukins, and colony-stimulating factors.

Biological therapies may be used to stop, control, or suppress processes that permit cancer growth; make cancer cells more recognizable, and therefore more susceptible to destruction by the immune system; boost the killing power of immune system cells, such as T cells, NK cells, and macrophages; alter cancer cells' growth patterns to promote behavior like that of healthy cells; block or reverse the process that changes a normal cell or a precancerous cell into a cancerous cell; enhance the body's ability to repair or replace normal cells damaged or destroyed by other forms of cancer treatment such as chemotherapy or radiation, and prevent cancer cells from spreading to other parts of the body. Some biological therapies are being used alone or in combination with other treatments such as radiation therapy and chemotherapy.

Angiogenesis Inhibitors in the Treatment of Cancer
Angiogenesis plays an important role in the growth and spread of cancer. New blood vessels "feed" the cancer cells with oxygen and nutrients allowing these cells to grow, invade nearby tissue, spread to other parts of the body, and form new colonies of cancer cells.

Scientists are trying to find ways to stop angiogenesis. They are studying natural and synthetic angiogenesis inhibitors (also called anti-angiogenesis agents) in the hope that these chemicals will prevent the growth of cancer by blocking the formation of new blood vessels. In animal studies, angiogenesis inhibitors have successfully stopped the formation of new blood vessels causing the cancer to shrink and die. Whether angiogenesis inhibitors will be effective against cancer in humans is not yet known. The process of producing and testing is likely to take several years.