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News — In the battle against breast cancer, medicine may be shooting at the wrong enemy. Much like using a weed-whacker to remove the top of lawn weeds, leaving the root behind, conventional treatments that target mature, late-acting cancer cells may miss early cells that can give rise to cancer recurrences.

Mammary stem cells that grow in human breast tissue may play a pivotal role in breast cancer, according to research to be presented at the International Association for Breast Cancer Research, sponsored by UC Davis Cancer Center. By developing novel molecular therapies to target these stem cells, medicine may be able to overcome the drug resistance and relapse that can inhibit successful breast cancer treatment. Even after apparently successful treatment, currently as many as 40 percent of breast cancer patients eventually experience a recurrence of their disease.

"It's been hypothesized for some time that there are stem cells in human cancers that are capable of dividing and taking on specific functional properties that may give cancers the ability to spread more readily or to evade standard therapies," said Alexander Borowsky, a breast cancer researcher at the UC Davis Center for Comparative Medicine. "Researchers now have found some ways to identify these cells in tumors — essentially creating a new field of cancer research."

Advances in the new field will be reported by research teams from throughout the world during the five-day meeting, which focuses on developments in the use of mouse models to study human breast cancer. Stem cells are young, unspecialized cells that have the potential to develop into a variety of different cell types.

On Tuesday afternoon, investigators from the University of Michigan Comprehensive Cancer Center in Ann Arbor will report on landmark experiments in which they successfully grew breast cancer tissue from both human and mouse mammary stem cells. The stem cells had been transplanted into the chests of specially bred laboratory mice.

"Utilizing conventional breast cancer therapies, we can produce a partial response in many women. But if we're leaving behind cells that can make the cancer return, we may be focusing on the wrong cells," said Max Wicha, director of the Michigan center. "We now have a validated new target for what we hope will be the development of more effective agents utilizing biological approaches."

In a related presentation the same afternoon, a team of investigators from Baylor University Medical School in Houston, UC San Francisco, Washington University School of Medicine in St. Louis, Mo., and Memorial Sloan Kettering Cancer Center in New York will present basic new insights into what causes stem cells to become malignant.

"Our findings, for the first time in laboratory animal models, demonstrate the differences between normal and cancer stem cells," said lead investigator Jeffrey Rosen, professor of molecular and cellular biology at Baylor University Medical School in Houston. Ultimately, the research team hopes to be able to develop drugs that can prevent mutated stem cells from reproducing and forming tumors.

According to Borowsky, the new field of cancer stem cell research could transform cancer treatment. "It will be very interesting to learn more about the properties of these cancer stem cells," he said. "How do they evade the body's natural defenses against cancer, and to what extent do they evade conventional cancer therapies? Can we fool them into differentiating into harmless, non-cancerous tissues? Can we specifically target these cells for destruction?"

The UC Davis Cancer Research Program encompasses the UC Davis Center for Comparative Medicine, a collaborative research venture of the UC Davis Schools of Medicine and Veterinary Medicine that focuses on diseases common to humans and animals, and the UC Davis Mouse Biology Program, home of the Mutant Mouse Regional Resource Center, the world's largest archive of mutant mice.

Founded in the mid 1950s, the International Association for Breast Cancer Research is an international community of scientists focused on the important issues in modern breast cancer research. The 24th IABCR Congress, devoted to preclinical research using mouse models of human breast cancer, is co-sponsored by the Office of Women's Health of the U.S. Department of Health and Human Services, the California Breast Cancer Research Program, and the National Cancer Institute's Mouse Models of Human Cancers Consortium and Specialized Programs of Research Excellence.

For information about other scientific presentations at the meeting, visit the conference Web site at .