Biological Therapies for Cancer: Questions and Answers
7. What are monoclonal antibodies? continued...
MOABs may be used in cancer treatment in a number of ways:
MOABs that react with specific types of cancer may enhance a patient's immune response to the cancer.
MOABs can be programmed to act against cell growth factors, thus interfering with the growth of cancer cells.
MOABs may be linked to anticancer drugs, radioisotopes (radioactive substances), other BRMs, or other toxins. When the antibodies latch onto cancer cells, they deliver these poisons directly to the tumor, helping to destroy it.
MOABs carrying radioisotopes may also prove useful in diagnosing certain cancers, such as colorectal, ovarian, and prostate.
Rituxan® (rituximab) and Herceptin® (trastuzumab) are examples of MOABs that have been approved by the FDA. Rituxan is used for the treatment of non-Hodgkin lymphoma. Herceptin is used to treat metastatic breast cancer in patients with tumors that produce excess amounts of a protein called HER-2. (More information about Herceptin is available in the National Cancer Institute (NCI) fact sheet Herceptin® (Trastuzumab): Questions and Answers, which can be found at http://www.cancer.gov/cancertopics/factsheet/Therapy/herceptin on the Internet.) In clinical trials, researchers are testing MOABs to treat lymphoma, leukemia, melanoma, and cancers of the brain, breast, lung, kidney, colon, rectum, ovary, prostate, and other areas.
8. What are cancer vaccines?
Cancer vaccines are another form of biological therapy currently under study. Vaccines for infectious diseases, such as measles, mumps, and tetanus, are injected into a person before the disease develops. These vaccines are effective because they expose the body's immune cells to weakened forms of antigens that are present on the surface of the infectious agent. This exposure causes the immune system to increase production of plasma cells that make antibodies specific to the infectious agent. The immune system also increases production of T cells that recognize the infectious agent. These activated immune cells remember the exposure, so that the next time the agent enters the body, the immune system is already prepared to respond and stop the infection.
Researchers are developing vaccines that may encourage the patient's immune system to recognize cancer cells. Cancer vaccines are designed to treat existing cancers (therapeutic vaccines) or to prevent the development of cancer (prophylactic vaccines). Therapeutic vaccines are injected in a person after cancer is diagnosed. These vaccines may stop the growth of existing tumors, prevent cancer from recurring, or eliminate cancer cells not killed by prior treatments. Cancer vaccines given when the tumor is small may be able to eradicate the cancer. On the other hand, prophylactic vaccines are given to healthy individuals before cancer develops. These vaccines are designed to stimulate the immune system to attack viruses that can cause cancer. By targeting these cancer-causing viruses, doctors hope to prevent the development of certain cancers.
Early cancer vaccine clinical trials involved mainly patients with melanoma. Therapeutic vaccines are also being studied in the treatment of many other types of cancer, including lymphoma, leukemia, and cancers of the brain, breast, lung, kidney, ovary, prostate, pancreas, colon, and rectum. Researchers are also studying prophylactic vaccines to prevent cancers of the cervix and liver. Moreover, scientists are investigating ways that cancer vaccines can be used in combination with other BRMs.