Cancer preventive vaccines are similar to traditional vaccines, which help prevent infectious diseases such as measles or polio by protecting the body against infection. Cancer vaccines target infectious agents that cause or contribute to the development of cancer. A new generation of vaccines can protect girls and young women from a virus that precipitates cervical cancers.
Why should I be aware of this?
- Potential cancer vaccines have had a long-and checkered history in which various clinical trials have badly failed.
- At the same time, scientists have labored for years on a wholly different approach that recruits immune molecules to treat cancers instead of preventing them. The theory is that such vaccines might be less toxic and more successful than other cancer treatments such as chemotherapy and radiation. 
- Rather than writing off cancer immunotherapy, some researchers argue that the agents have been examined in the wrong way, resulting in erroneous conclusions. With the correct study design, proponents say, cancer vaccines should prove to be promising.
All about cancer vaccines
Cancer vaccines belong to a class of substances known as biological response modifiers which work by stimulating or restoring the immune system’s ability to fight infections and disease. There are two broad types of cancer vaccines:
- Preventive (or prophylactic) vaccines. These are intended to prevent cancer from developing in healthy people; and
- Treatment (or therapeutic) vaccines. These are intended to treat already existing cancers by strengthening the body's natural defenses against cancer.
Two types successfully developed
Two types of cancer preventive vaccines have been successfully developed and are available in the United States.
The U.S. Food and Drug Administration (FDA) approved the vaccine known as Gardasil® in 2006. This vaccine protects against infection by two types of HPV — specifically, types 16 and 18. These types of HPVs cause approximately 70 percent of all cases of cervical cancer worldwide.
At least 17 other types of HPV are responsible for the remaining 30 percent of cervical cancer cases . Gardasil also protects against HPV types 6 and 11, which cause about 90 percent of all cases of genital warts. However, these two HPV types do not cause cervical cancer.
In 2008, the FDA expanded Gardasil’s approval to include its use in the prevention of HPV-associated vulvar and vaginal cancers.
A second HPV vaccine manufactured by GlaxoSmithKline and known by the name Cervarix® has also been developed. In contrast with Gardasil, Cervarix is a bivalent vaccine. It is composed of VLPs made with proteins from HPV types 16 and 18. Therefore, it provides protection only against these two HPV types.
Public health benefits
The public health benefits of vaccines against HPV types 16 and 18 may extend beyond reducing the risks of cervical cancer, vaginal cancer, and vulvar cancer. Evidence suggests that chronic infection by one or both of these virus types is also associated with cancers of the anus, penis, and oropharynx.
The FDA has approved one other type of cancer preventive vaccine, which protects against HBV infection. Chronic HBV infection can lead to liver cancer. The first HBV vaccine was approved in 1981, making it the first cancer preventive vaccine to be successfully developed and marketed. Today, most children in the United States are vaccinated against HBV shortly after birth .
How vaccines work
Cancer treatment vaccines are designed to delay or stop cancer cell growth; cause tumor shrinkage; prevent cancer from coming back; or eliminate cancer cells that are not killed by other forms of treatment, such as surgery, radiation therapy, or chemotherapy.
A detailed understanding of how immune system cells and cancer cells interact is necessary to develop effective cancer treatment vaccines. The immune system often does not “see” cancer cells as dangerous or foreign, as it generally does with microbes. For this reason it does not mount a strong attack against the cancer cells.
The main reason why the immune system does not easily recognize the threat posed by an already growing cancer is because the cancer cells carry normal self antigens in addition to any cancer-associated antigens. Furthermore, cancer cells sometimes undergo genetic changes that lead to the loss of cancer-associated antigens. Apart from these, cancer cells can produce chemical messages that suppress specific anticancer immune responses by killer T cells. As a result, even when the immune system recognizes a growing cancer as a threat, the cancer may still escape a strong attack by the immune system.
- Cancer treatment vaccines are designed to treat cancer by stimulating the immune system to recognize and attack cancer cells. 
- Effective cancer treatment vaccines are difficult to develop because some cancers can escape detection by the immune system or weaken natural immune responses against cancer cells. 
- Researchers are developing treatment vaccines against many types of cancer and testing them in clinical trials. 
- The side effects of cancer vaccines vary from patient to patient and according to the type of vaccine being used. Most of the side effects reported thus far have been mild and limited to inflammation at the site of the vaccine injection. 
Therapeutic cancer vaccines received a potentially big boost this week when Seattle-based biotech company Dendreon announced that its Provenge vaccine prolonged the lives of prostate cancer patients. The success of this trial could pave the way for approval of the drug, which triggers the body's immune system to attack malignant prostate tumors.