Emma Patten, (Medical Writer)

To treat a tumor in the 1890s, the doctor may have ground up some tumor tissue, mixed it with tuberculosis-causing organisms, and plunged a needle with the mixture into the tumor. It sounds pretty awful, but this "vaccine" actually shrank tumors in a few patients who survived the probable tuberculosis infection. Perhaps these doctors of yesteryear weren't so far off the mark.These days, cancer vaccines have been enjoying a surge of popularity as promising weapons in the war against cancer.
　　
Vaccines may one day prove even better than chemotherapy for the treatment of certain cancers.
"We are starting to get to some of the basic biology behind the development of these vaccines," says Dr. Barry L. Gause, a research scientist with the National Cancer Institute in Bethesda, Maryland. "It's only been since the late 1970s, when we really learned a lot about the immune system, that people have been able to target the immune response to tumors. Now it's becoming very high-tech," he adds. 
Some oncologists now view immunotherapy (such as cancer vaccines) as the fourth method of treating cancer, after surgery, radiation, and chemotherapy. Most cancer vaccines are in their infancy. 
　　
Self Versus Non-self
The problem with the immune system is that it sometimes fails to recognize cancer cells as being "non-self." Although a cancer cell grows abnormally, the cell nonetheless stems from a person's own body, and the immune system does not necessarily recognize it. But sometimes cancer cells do have distinctive features that can help the vaccine target the cell.
Unlike chemotherapy, vaccines may be able to target cancer cells, sparing the normal cells.　　
　　
Prostate cancer cells, for example, bear a specific "non-self" target called prostate specific antigen. Researchers are now looking into using a small part of it to make a vaccine. Similarly, vaccines are being tested against other cancer cells with distinctive markers that cause melanoma, and breast, kidney, and colon cancers.
Vaccines may one day prove even better than chemotherapy for the treatment of certain cancers. Unlike chemotherapy, which kills both normal and cancerous cells, vaccines may be able to target cancer cells, sparing the normal cells.
Professor of biological sciences Suzanne Ostrand-Rosenberg at the University of Maryland, Bethesda, is optimistic about the future role of vaccines. "I think that vaccines are going to play a role that chemotherapy can't play at this point," she says. "By its nature, chemotherapy is not really that specific so it has a lot of side effects on normal tissues. Vaccines, on the other hand, if they can be fine-tuned, should be able to single out malignant cells. Therefore you could presumably use doses that would target cancer cells and not normal cells."

Vaccines Are Limited
But even when a specific target exists on a cancer cell, vaccines are limited in what they can attack, primarily because of the bulkiness of more advanced tumors. Ostrand-Rosenberg explains that because of the sheer mass of advanced tumors, vaccines cannot reduce their size the way chemotherapy can.
Dr. Gause says, "Vaccines work best in patients that have very low volumes of disease. They would either be more effective in someone who has had cancer before and you know that they are at increased risk of the disease coming back, or a person who is already at an increase risk of cancer." So far, experts agree that vaccines work better when used in combination with traditional methods of treatment like chemotherapy or surgery.

A Universal Vaccine
It may also be unlikely that a single miracle vaccine will ever be able to wipe out all types of cancer. "Cancer is a multitude of diseases that have certain biological properties that are the same, but the diseases themselves are quite different," explains Dr. Gause. "In order to have one type of treatment for all types of cancer, there has to be a common target, and so far there is no such animal."
Others think that a universal vaccine is possible, however. Dr. Maurizio Zanetti of the University of California, San Diego is studying a molecule called telomerase, which is present in normal cells, but overexpressed in cancerous cells and allows the cells to keep dividing. "The ideal situation is to define molecules that are expressed selectively in all types of cancer. And that one molecule, for the time being, is telomerase," Dr. Zanetti says. "I suspect that there are now many laboratories trying to develop the same idea."

Researchers agree that it's impossible to predict where the future is headed. "Many laboratories are working very hard on trying to develop these vaccines, and I think that there's certainly enough experimental data that shows that under some circumstances they do work," says Ostrand-Rosenberg. "The question is that we don't fully understand why they don't work all the time or why they don't work better under some circumstances," she says. "We can't predict, but people are really working very hard at this."

(From ABCNEWS.com)