Biological therapy approaches vary, but all try to help the immune system recognize cancer cells as foreign invaders. The various drugs used in these treatments are known as biological response modifiers (BRMs). They include:

• Interferons (IFNs). A drug that mimics a type of cytokine, a protein that activates certain immune system cells and is made by the body. The three types of interferon are interferon alpha, interferon beta and interferon gamma. Interferon alpha is the type most commonly used in cancer treatment. These medications boost interferon levels to slow the growth of cancer cells and stimulate the immune system to fight cancer cells. They also help promote the transition of cancer cells into cells that behave more normally. Some interferons may boost the immune system’s anticancer function by stimulating various immune system cells such as NK cells, T cells and macrophages.
  
  Interferon alpha was the first cytokine known to have an antitumor effect. Researchers are testing the anticancer effects of interferon beta and interferon gamma. All the interferons are being studied for effectiveness when combined with other cytokines and chemotherapy. 
• Interleukins (ILs). As with interferons, these drugs are produced in a laboratory to mimic a cytokine made naturally by the body. While more than a dozen interleukins have been developed, only interleukin-2 (IL-2) has been approved by the U.S. Food and Drug Administration (FDA) for treatment of cancer. IL-2 helps boost production and stimulate certain white blood cells, especially T cells. This gives the immune system more power in identifying and attacking cancer cells. Other interleukins are being studied in clinical trials.
  
  Some researchers are experimenting with IL-2 by removing T cells from a patient’s body, creating additional T cells in a laboratory and stimulating them with IL-2. The cells then are returned to the body in greater numbers than the human body can produce on its own. Early results have shown promise. 
  
• Monoclonal antibodies (MOABs). An artificial antibody (protein that fights infections) that can be targeted against specific areas of cancer cells. The MOABs are injected into the body, where they attach to the area for which they were made, most often on the surface of certain cancer cells. When this occurs, it helps the body recognize the cancer cells as foreign, triggering the immune system to detect and attack the cells. In addition, MOABs can act directly against cancer cells and interfere with their growth and development.
  
  To create these drugs, scientists first inject human cancer cells into mice. When the mice make antibodies to these cells, the mouse plasma cells that produce the antibodies are removed and fused with laboratory–grown cells. This creates hybrid cells called hybridomas, which produce large quantities of monoclonal antibodies.
  
  MOABs may be used to treat cancer in the following ways:
  
  
  • Enhance a patient’s immune response to a specific cancer
    
    
  • Interfere with the growth of cancer cells
    
    
  • Binding and delivering radioactive substances, anticancer drugs and toxins directly to tumor cells to help with destruction 
    
  • Enhance a patient’s immune response to a specific cancer
    
    
  • Interfere with the growth of cancer cells
    
    
  • Binding and delivering radioactive substances, anticancer drugs and toxins directly to tumor cells to help with destruction 
    

  However, monoclonal antibodies can only travel a few cell layers deep from where blood vessels enter a tumor. As a result, they do not kill cancer cells that are distant from a blood vessel. Clinical research continues on methods to improve the cancer–fighting effectiveness of monoclonal antibodies.

  Examples of MOABs approved by the FDA include Rituxan (most often used in lymphomas) and Herceptin (shown to be effective in both treating and preventing recurrences of breast cancer).

• Colony-stimulating factors (CSFs). Sometimes called hematopoietic growth factors, these drugs stimulate bone marrow stem cells to divide and develop into white blood cells, red blood cells and platelets. Bone marrow is important to the immune system because it is the source of all blood cells. It is often damaged in treatments such as radiation therapy and chemotherapy, decreasing the effectiveness of the immune system. Thus, the ability of CSFs to stimulate the production of these cells may allow physicians to increase the dose of anticancer drugs without the risk of infection or need for blood transfusions. Filgrastim and erythropoietin are examples of hematopoietic growth factors.
• Nonspecific immunomodulating agents. Substances that stimulate and indirectly augment the immune system. These agents act directly on immune system cells and cause secondary responses such as increased cytokine and antibody production. For example, Bacillus Calmette Guerin (BCG) is a vaccine for tuberculosis that is also used to treat some forms of bladder cancer and colorectal cancer.
  
  
  Antiangiogenesis is a new biological therapy that shows promise in fighting cancer. This strategy prevents tumors from generating new, small blood vessels necessary for the tumor to sustain itself. Several chemicals and antibodies have shown the ability to block angiogenesis, theoretically making it possible to shrink the tumor. While these drugs generated considerable early excitement, the first clinical trials were disappointing. Since then, researchers have reassessed antiangiogenesis drugs, and now they are usually considered add-on therapies to traditional drugs. Several have been approved by the FDA since 2004.
  
  
• Epithelial growth factor receptor (EGFR) inhibitors. EGFR has been associated with aggressive cancer cell growth in tumors. EGFR inhibitors are drugs that may help prevent the development and progression of cancer in certain tumors. Recent research has shown that the EGFR inhibitor lapatinib may improve survival rates in patients with advanced breast cancer, when it is combined with chemotherapy. Other studies of lapatinib to treat kidney cancer have produced mixed results.
  
  
• Gene therapy. This treatment is based on altering a cell's genetic material to fight or prevent disease. It is an experimental method that involves introducing genetic material, such as DNA, into an individual’s cells to fight cancer. Some approaches of gene therapy target the destruction of cancer cells to prevent their growth. Other forms of gene therapy focus on increasing the ability of healthy cells to fight cancer. Gene therapy is currently available only in clinical trials.
  
  There are several techniques being studied with gene therapy. Researchers are evaluating the replacement of missing or altered genes with healthy genes. In another approach, researchers are injecting cancer cells with genes that can be used to destroy the cells or genes that can make the cells more sensitive to chemotherapy and radiation therapy. Scientists continue to study additional uses of gene therapy in cancer treatment.
   

• Cancer vaccines. Cancer vaccines fall into two categories: those that treat existing cancers and those that aim to prevent future cancers from forming. Treatment vaccines work by sensitizing the immune system to antigens on the surface of cancer cells, causing the body to attack and destroy the cancer cells. Normally, the body does not recognize cancer cells as "foreign" and does not attack them, and cancer cells have often developed sophisticated ways to avoid the immune system. Currently, no treatment vaccines have been approved by the FDA, but there are several large-scale clinical trials focused on cancer vaccines.

  Vaccines that aim to prevent cancer have so far focused on viruses that are linked to cancers. The FDA has approved two of these vaccines, including one that prevents hepatitis B, which is linked to liver cancer, and one that prevents four strains of human papillomavirus (HPV), two of which are linked to 70 percent of cases of cervical cancer.