WASHINGTON (AP) _ Only a small percentage of breast cancer cells appear capable of spreading the disease, a finding that researchers hope will lead to ways to target the most dangerous cells.
A study done at the University of Michigan Comprehensive Cancer Center found that between 1 percent and 15 percent of cancer cells were capable of forming new malignant tumors.
Dr. Max S. Wicha, who was part of the research team, said the finding helps point the way to more effective treatments.
``What we are working on now is finding out what makes these tumor stem cells different from the other cells in a tumor,'' he said. ``Now that we can actually identify them, we can start developing treatments to specifically target and hopefully eliminate them.
The findings are reported in Tuesday's online edition of Proceedings of the National Academy of Sciences.
``The first step was to identify the cells, the next step is to try to find out what makes them tick and then to target them with new therapies,'' said Dr. Michael F. Clarke, who led the team.
Tests showed that these cells were able to develop into various types of cells present in a tumor, somewhat like a stem cell can develop into any of a number of normal tissues in the body.
Like stem cells, these dangerous cancer cells ``make copies of themselves _ a process called self-renewal _ and produce all the other kinds of cells in the original tumor,'' Clarke said.
Similar cells have been identified in human leukemia, but these are the first to be found in solid tumors, Clarke said. He said the researchers plan to begin looking at other types of cancer to see if they also have similar danger cells.
For women with cancer, Wicha said, ``for the first time, we can define what we believe are the important cells _ the cells which determine whether the cancer will come back or be cured. Before this, we didn't even know there were such cells.''
Clarke emphasized that ``this is not a cure for cancer. But it is a very promising lead, which will focus our efforts to try to find a cure for cancer.''
Dr. Dawn Willis, scientific program director for the American Cancer Society, said the findings are ``a very interesting observation, but it is still a long way from clinical usefulness.''
Clarke agreed that their work is some steps away from clinical use. He said they hope to find pathways to target the danger cells this year _ but finding the chemicals to attack those targets and developing ways to use them could take five to 10 years.
The researchers used breast cancer cells removed from patients and sorted the cells into groups according to the proteins present on the surface of the cells. They then injected the cells into the mammary glands of mice.
The one cell type that consistently caused tumors to develop had a protein called CD44 and little or none of a protein called CD24, they reported.
``As few as 100 to 200 of these tumor-inducing cells, isolated from eight of nine tumors in the study, easily formed tumors in mice, while tens of thousands of the other cancer cells from the original tumor failed to do so,'' Clarke said.
The University of Michigan has applied for a patent on the identity and function of tumor stem cells.