SAN FRANCISCO (Reuters) - Medical researchers said they have developed a vaccine that targets breast cancer tumors before they become malignant, possibly marking an effective new therapy for controlling the disease. Dr. Laura Esserman, director of the University of California-San Francisco Breast Care Center, said the new vaccine could help prevent tumors from developing into invasive breast cancer. The vaccine strategy targets HER2/neu, a specific protein found in many breast cancer tumors that eventually progress to malignancy. Doctors estimate that 10 to 15 percent of the 180,000 women who get breast cancer each year are diagnosed with tumors at this pre-malignant stage, known as ductal carcinoma in situ (DCIS), and that up to 30 percent of these lesions are likely to progress to malignancy even after lumpectomies. Esserman's team tested its vaccine on lab mice predisposed to mammary gland tumors and found that only about 50 percent of the animals immunized against the HER2/neu developed cancer, compared with some 90 percent of nonimmunized mice. "We need less invasive strategies for women who are detected with very early cancers, and we will need new models to test this in women," Esserman said.