08/23/2010 05:13 pm ET | Updated May 25, 2011

Cancer Vaccines: Not One Size Fits All

Often, when people talk about a "cure" for cancer, they seem to be picturing something like the vaccine for smallpox or polio: a single shot that will eradicate the deadly killer once and for all. And although there are efforts underway to create a universal vaccine that "releases the brakes" from the immune system so that it can launch an attack against malignant cells (more about this later), it's more likely that the "cure" for cancer will turn out to be a collection of incremental advances that allow scientists to develop highly individualized treatment programs for a particular kind tumor or specific stage of a cancer.

While this scenario might be less broad-stroke than we would wish, it might prove to be more successful in the long run since it's consistent with the nature of the disease, which is so diverse and has so many different ways of originating. Cancer can result from genetic damage that causes a normal cell to divide abnormally or, in the case of aberrant tumor suppressor genes, to allow cancer to develop instead of preventing it. Chromosomal abnormalities that cause genes to be missing, duplicated or rearranged can cause a predisposition to cancer. Viruses can be factors as well. The Epstein-Barr virus has a correlation to Burkitt's lymphoma, human papillomavirus types 16 and 18 cause cervical cancer, and hepatitis B is associated with liver cancer. Immune diseases like AIDS can create a vulnerability to certain cancers including Kapoli's sarcoma and lymphoma. Cancer can also be caused from exposure to carcinogenic elements in the environment like asbestos, coal or formaldehyde. Then there are the "lifestyle" carcinogens we voluntarily expose ourselves to, like alcohol, tobacco, smokeless tobacco and UV rays from the sun or tanning beds.

What Is Cancer?
Complex as this disease is, the short answer is that it develops when cells divide at an abnormally accelerated rate until they form a mass of tissue called a tumor. As the tumor enlarges, it destroys normal tissue. The tumor gets nutrients from neighboring blood vessels, but can also make blood vessel-forming factors that can allow a tumor to grow its own blood supply. As tumor cells invade those blood vessels, they may be transported (metastasize) to other areas of the body.

Cancer Therapies
So far, no single therapy has been able to succeed against this varied, mobile and highly resourceful disease. Surgery is the oldest therapy and still prescribed as one element of treatment for most patients with solid tumors like breast, lung, stomach or kidney cancer. Radiation is often used in conjunction with surgery, either to shrink the tumor before surgery or to kill residual tumor cells. The downside is that radiation also attacks normal cells and causes debilitating side effects like fatigue and nausea. Chemotherapy uses drugs to attack cancer cells, but can also have extreme side effects like hair loss, fatigue and severe nausea because these therapies also are toxic to normal cells. A new class of drugs referred to as "targeted therapies" have been designed to attack specific cellular abnormalities that been identified in some cancers. They are generally less toxic than the less specific chemotherapy drugs. Hormone therapy is used to treat some hormone-sensitive tumors like breast and prostate cancer.

New Possibilities
More in line with hormone therapy is a new focus on immunotherapy (the use of cancer vaccines and treatments that boost the body's own immune system) as a viable treatment option. But cancer vaccines are different from traditional vaccines in that they don't create immunity like they do for smallpox or polio. Rather, they "train" the immune system to retaliate against an existing tumor or cells that are behaving abnormally. (The human papillomavirus vaccine is an exception because it helps prevent the development of cervical cancer.) By programming immune cells like T-lymphocytes to recognize and attack the cancer, vaccines can increase efficacy while substantially diminishing side effects since they affect only the cancer cells, not the surrounding healthy tissue. But because every cancer tends to be different, vaccines have to be customized for each patient or tumor type. Some are even targeted to certain stages of the disease. The new FDA-approved cancer vaccine for prostate cancer, Provenge, uses the patient's own immune system to fight advanced prostate cancer that has stopped responding to hormone therapy.

Clinical trials are also proceeding on a vaccine for brain tumors (glioblastoma multiforme) that targets specific antigens on cancer stem cells. And while this therapy would also be highly specialized, similar elements on malignant cells have shown that antibodies in the glioblastoma vaccine may be applicable to small cell lung, pancreatic and ovarian cancer, as well as multiple myeloma.

The many vaccines in development include an immune booster, the one I mentioned earlier, that works by blocking a protein that stops T-lymphocyte cells from attacking cancer cells. And although it's more of a universal therapy, this vaccine is also being tested against lung and prostate cancer, as well as stage 4 melanoma. Though these trials are not providing the cancer cure all we all dream about, even small advances are welcome in this battle.

Through perseverance and flexibility in our thinking, the answer may be more like a mosaic, a compilation of small, highly targeted therapies that together become the true picture of the cure.