Work Continues on Breast Cancer Vaccine

(March 19, 2008) - Researchers say they are making some progress on breast cancer vaccine. (Read about "Breast Cancer") The latest study has shown that vaccinating mice with a modified form of a virus containing proteins from breast cancer cells can kill large breast cancer tumors and tumors that have spread to the lungs. The rodent model of cancer used in this study closely resembles a type of breast cancer seen in humans called HER2-positive. Although other cancer vaccines have shown activity in the treatment of very small tumors, their ability to influence large, established tumors, such as many HER2-positive breast cancers, has proven difficult. The study, led by researchers at the National Cancer Institute (NCI) appeared in Cancer Research.

Therapeutic cancer vaccines are intended to disrupt new or existing cancerous growth by stimulating the body's immune system so that it recognizes the cancer as an invader. These vaccines use certain protein molecules on the surface of cancer cells, such as the HER2 receptor protein, as the triggers to initiate an immune response. (Read about "The Immune System")

The modified virus used as a vaccine in this study showed activity against ErbB2-positive tumors. The ErbB2 gene is known as HER2 in humans, and neu is its counterpart in mice. Approximately 20 percent to 25 percent of breast cancers in women are HER2-positive and tumors overexpressing the HER2 receptor protein are more aggressive and more likely to recur than tumors that do not overexpress the protein. Thus, the HER2 receptor protein is an important target.

"A therapeutic vaccine may offer an advantage over treatments, such as monoclonal antibodies, that target a single site on a cancer cell because it may induce the production of several different antibodies that can target multiple regions on a receptor, making it harder for the tumor to mutate and escape the effects of therapy," said Jay A. Berzofsky, M.D., Ph.D., of the Vaccine Branch at NCI's Center for Cancer Research (CCR).

The researchers observed that the tumors were smaller seven days after vaccination; all the tumors had disappeared between 25 and 45 days after the mice were vaccinated. The mice remained tumor-free through the end of the study.

The researchers also looked at the effects of the vaccine on tumors of different sizes. They found that although tumors as large as 2 cubic centimeters continued to grow for seven days after immunization, these tumors did begin to regress by 10 days and disappeared about 30 days after a single vaccination. In a separate experiment, the researchers observed that tumors as large as 3.5 cubic centimeters disappeared after a single dose. Vaccination, however, was not sufficient to treat tumors larger than 5.5 cubic centimeters. Although these tumors did shrink, they started to regrow two weeks after a single vaccination.

Related Information:

    Cancer: What It Is

    Cancer Treatments