A University of California-San Francisco researcher has developed a vaccine that could prove to be an effective tool in the fight against breast cancer, university officials announced.

The vaccine targets a specific protein common in pre-malignant breast cancer tumors. About 10 percent to 15 percent of the 180,000 women who get breast cancer each year are diagnosed in this pre-malignant stage.Mice injected with the vaccine developed antibodies and were less likely to develop cancerous tumors, said Dr. Laura Esserman, director of the UCSF Breast Care Center and a nationally recognized breast cancer researcher.

The study suggests that the vaccine might prevent pre-malignant lesions called ductal carcinoma insitu, or DCIS, from becoming invasive breast cancer in humans, said Esserman, who presented her findings Thursday at the San Antonio Breast Cancer symposium.

"We believe that the very early diagnosis of a cancer may be the ideal time to intervene with a preventive strategy, such as a vaccine," Esserman said.

An estimated 10 percent to 50 percent of women who have the pre-malignant tumors go on to develop breast cancer, Esserman said. Too often, women who find out they have the early form of the disease respond by choosing the most radical method of treatment: mastectomy. With a vaccine to stop the cancer in its tracks, such a step would not be necessary, she said.

"Instead of being frightened by having one of these early lesions," Esserman said, "all of a sudden you have a nontoxic alternative that will make you feel safer."

Esserman said she hopes to secure a grant for human testing of the vaccine, which could begin in three years.

Unlike vaccines that prevent illness, cancer vaccines are designed to fight illnesses that already exist and prevent cancers from spreading, thereby prolonging life.

Esserman's vaccine is among several now being developed for breast cancer and, if effective, might work on more advanced cancer as well, she said.