WASHINGTON (AFP) ― Scientists in the United States said Monday they have developed a vaccine that attacks tumors in mice, a breakthrough they hope will help fight breast, colon, ovarian and pancreatic cancer in humans.

Although studies on mice often do not translate directly into remedies that work for human subjects, researchers are hopeful because of the strength of the vaccine and the particular approach it takes.

“This vaccine elicits a very strong immune response,” said study co-senior author Geert-Jan Boons, a professor of chemistry and a researcher in the University of Georgia Cancer Center.

“It activates all three components of the immune system to reduce tumor size by an average of 80 percent.”

The vaccine works by training the immune system to attack tumors that have a protein known as MUC1 on the surface of their cells, according to the study published in the Proceedings of the National Academy of Sciences.

MUC1 is found on more than 70 percent of the most aggressive and lethal types of cancer, including most kinds of breast, pancreatic, ovarian and multiple myeloma.

“This is the first time that a vaccine has been developed that trains the immune system to distinguish and kill cancer cells based on their different sugar structures on proteins such as MUC1,” said study co-author Sandra Gendler, professor at the Mayo Clinic in Arizona.

The protein is also overexpressed in 90 percent of breast cancer patients with so-called “triple negative” tumors that do not respond to hormonal therapy such as Tamoxifen, aromatase inhibitors, or the drug Herceptin.

These patients urgently need a new approach to their cancers.

“In the U.S. alone, there are 35,000 patients diagnosed every year whose tumors are triple-negative,” Boons said.

“So we might have a therapy for a large group of patients for which there is currently no drug therapy aside from chemotherapy.”

A vaccine against MUC1 could be used in combination with chemotherapy, or as a preventive measure in patients at high risk for certain cancers.

Boons, Gendler and colleagues are currently at work testing the vaccine on human cancer cells in the lab, and could begin phase I clinical trials to test the safety of the vaccine by late 2013.