A vaccine is a very common way of building up the immune system to fight infection. Using vaccines to fight breast cancer is relatively new, however, and still considered experimental. A vaccine for breast cancer may consist of an antigen cocktail of weakened or essentially dead elements of breast cancer cells that could stimulate an antibody response. The cancer vaccine might be prepared from your own deactivated cancer cells, or from extracts of breast cancer cells cultivated in a laboratory. Vaccines like this are only available in clinical trials.
But as soon as these vaccines are proven effective and win FDA-approval, they will become available outside of clinical trials. The vaccine is given by injection (usually under the skin). Once your immune system becomes aware of the antigens in the vaccine, it responds by making antibodies. Hopefully these antibodies will able to attack and destroy any remaining cancer cells. Later, if any new cancer cells appear, the circulating antibodies of the vaccine-educated immune system would destroy them also.
The Challenges of Cancer Vaccines Although vaccines have a strong track record in fighting many serious infections (such as polio, mumps, and measles), they are very much in the experimental stage for cancer. One problem is the way cancer progresses. It begins when one of your normal cells becomes abnormal and starts multiplying out of control, generation after generation. Each generation produces variations. Eventually the cancer has countless faces, with a limitless variety of antigens that need to be targeted by antibodies.
The cancer vaccine, however, results in a limited number of antibodies against the specific cancer cell antigens that were in the oroginal vaccine preparation. These antibodies may not be effective against the full range of newly developing cancer cells. In addition, an effective vaccine must summon antibodies that target the bad cells and leave normal cells alone. The trick is to catch the cancer cells as soon as they form, and make the vaccine with cancer cell parts that are not shared by normal cells. Researchers are investigating ways to identify cancer cells at this very early stage.
This could be done perhaps with chemicals that would tag the problem cells, and then alter them enough so that the immune system perceives them as abnormal and attacks them. Antibodies to fight cancer genes Another approach is to produce antibodies against specific cancer genes called Oncogenes. Normal oncogenes keep cell growth under control and suppress cancer by directing the production of a host of special proteins that conduct business as usual around the cell. Abnormal, malfunctioning oncogenes, however, such as a faulty HER2/neu gene, fail to regulate cancer cell growth, resulting in tumors.
These abnormal cancer genes or their related proteins provide a very precise target for an antibody. If the abnormal gene is only found in your cancer cells, and not in your normal cells, the antibody can do a good job destroying cancer cells, leaving the rest of you alone. An antibody therapy directed against the protein made by the oncogene HER2/neu, for instance, is Herceptin (chemical name: trastuzumab). While many of your tissues normally have HER2/neu present, it is in tiny amounts. Cancer cells that have too much HER2/neu protein around are bombarded by the Herceptin antibody (much, much more than any normal tissue).
This therapy represents a remarkable advance for women with HER2/neu–positive cancers, because it effectively treats the cancer with very few side effects to normal tissue. Another version of this approach is to deliver antibodies with attached poisons, such as nitrogen mustard or a radioactive agent, which helps kill the cancer cells. Studies of this technique in animals are encouraging, and clinical trials are ongoing. You might be reading this section and thinking, “Wow, this stuff sounds great, why isn’t this used more often? How come they haven’t perfected it already? ” We agree: antibody therapy holds great promise.
But there are two serious obstacles with the use of antibodies to target cancer cells. First, the size of the antibodies is important relative to the size of the cells. Some cancer cells are destroyed only if the antibody molecules can penetrate the cells’ outer (and sometimes inner) barriers. If they’re too big, the antibodies may not be able to get into the cells. The second problem is that with each generation of cancer cells that form, it’s hard to make antibodies that work effectively against all of the different kinds of cells that make up the cancer. Ongoing research will, it is hoped, overcome these problems.