SUNDAY, April 4, 2004 (HealthDayNews) -- The prospect of breast cancer vaccines -- from ones that would attack the cancer to others that would prevent it -- generates tremendous hope among cancer patients and their doctors.
But the reality, researchers say, is at least a decade away.
"Probably dozens of breast cancer vaccines are under study," says Dr. Robert Vonderheide, an assistant professor at the Leonard and Madlyn Abramson Family Cancer Research Institute at the University of Pennsylvania.
"It has been a huge area of research for a long time," he adds. "It's a goal over the next decade to have a vaccine against breast cancer. But it's important to recognize how long this will take."
To understand the urgency for a cancer vaccine, consider that the immune system doesn't see tumors as dangerous, so it fails to mount an aggressive attack against them, cancer experts say.
Vaccines that are being designed to treat existing cancers are called therapeutic vaccines, while those intended to prevent cancers are known as prophylactic vaccines, the National Cancer Institute (NCI) says.
Most therapeutic vaccines under development -- including those not just for breast cancer but for other cancers such as melanoma, lung, ovarian and prostate tumors -- focus on "kick-starting" the immune system. The goal: to prevent the further growth of existing cancers, block the recurrence of treated cancers or kill cancer cells not destroyed by previous treatment.
Currently, the only cancer-related vaccine approved by the U.S. Food and Drug Administration is a prophylactic vaccine for the hepatitis B virus, which is associated with liver cancer.
Yet, several breast cancer vaccines show preliminary promise. If the research bears fruit, it may be possible some day to administer such a vaccine to women at high risk for breast cancer.
"The majority [of breast cancer vaccines under study] are in the early stages," says Dr. Teresa Gilewski, a medical oncologist on the breast cancer service at Memorial Sloan-Kettering Cancer Center in New York City.
The first step is to perfect a therapeutic vaccine or vaccines that would treat women with breast cancer by preventing a recurrence of their disease or shrinking their tumors, Gilewski says.
Once that goal has been reached, researchers can focus on preventive vaccines, she says.
Using vaccines to treat breast cancer is still considered experimental, so there are several different approaches under review.
Vonderheide and his team, for instance, are studying the effectiveness of a telomerase peptide as a vaccine. "Telomerase is an enzyme," explains Vonderheide. "Tumor cells have more telomerase than found in normal cells. Our vaccine is designed to generate a particular kind of white blood cell." These blood cells should, in theory, attack the telomerase in the cancer cells, killing off the tumor, he says.
Vonderheide has started a Phase I clinical trial to evaluate the effectiveness of a telomerase peptide as a vaccine. The study will measure potential tumor cell shrinkage in women after an immune response has been triggered to the telomerase peptide, which is found in more than 90 percent of breast cancer tumors, the researchers say.
The type of therapeutic vaccine under review by Vonderheide falls under the category of antigen/adjuvant vaccines, the NCI says. These antigen vaccines use specific protein fragments or peptides to mobilize the immune system. Sometimes the antigens are combined with another substance -- known as an adjuvant -- that triggers an immune response.
Sometimes vaccines are made by taking cells from a patient's own tumor or from the tumor of other patients, and then these vaccines are used to bring about an immune response.
There are still other approaches, such as taking specialized white blood cells, known as dendritic cells, from a patient's blood through a process called leukapheresis. In a laboratory, these cells are stimulated with the patient's own cancer antigens, grown and then re-injected into the patient. The vaccine then activates cancer-fighting T-cells in the immune system, causing them to multiply and attack tumor cells that produce the antigen.
Gilewski's team is testing breast-cancer vaccines using a variety of synthetic antigens.
"Antigens can come from the patient's own tumor or from others' tumors," Gilewski says. Antigens can be peptides, proteins, carbohydrates, DNA or other substances, she says. "There may be numerous antigens in the same vaccine," she adds.
Whatever the antigen or antigens, she says, "you are giving the immune system something to react to."
Dr. Herman Kattlove, a spokesman for the American Cancer Society, calls the concept of breast cancer vaccines "wonderful." If cancer is to be cured when surgery doesn't work, he adds, "some kind of immunologic method will be necessary."
But he, too, cautions that vaccines are at early stages.
Vonderheide agrees. "There are many roadblocks and many questions to be answered," he says.