Breast Cancer :: Breast cancer stem cells resist radiation treatment

The population of breast cancer cells that gives rise to a tumor may be relatively resistant to radiotherapy and may even increase when given multiple treatments of radiation, a new study shows.

In the last several years, researchers have discovered a small population of so-called cancer-initiating cells (also called cancer stem cells) in several cancers. These cells can self-renew and maintain the growth of a tumor, whereas its daughter cells cannot. Scientists are studying the properties of cancer-initiating cells because the destruction of these cells is likely necessary for the successful treatment of a cancer.

To test the response of breast cancer-initiating cells to radiation treatment, Tiffany M. Phillips, William H. McBride, Ph.D., D.Sc., and Frank Pajonk, M.D., Ph.D., of the David Geffen School of Medicine at the University of California, Los Angeles, exposed such cells and normal breast cancer cells to a single or multiple doses of radiation.

More cancer-initiating cells survived radiation treatment than did the other breast cancer cells. For example, 46% of cancer-initiating cells survived treatment with 2 Gray of radiation compared with 20% of normal breast cancer cells. When cells were given clinical doses of radiation (3 Gray) each day for 5 days, the proportion of cancer-initiating cells increased. This, the scientists found, may happen because radiation treatment seems to activate a specific signaling pathway that prompts the cancer-initiating cells to self-renew.

In an editorial, Maximilian Diehn, M.D., Ph.D., and Michael F. Clarke, M.D., of the Stanford University School of Medicine, note that, among other limitations, the new study was conducted with tissue culture cells, which may not mimic the actual conditions of a tumor in a person. Nevertheless, the findings are provocative, they write. “The findings ? have important clinical implications. In light of [this and other studies], it is even clearer that identifying and characterizing [cancer stem cells] for every tumor possible is of paramount importance and will likely lead to new therapeutic avenues.”

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