Breast Cancer Stem Cells Are Radioresistant

Certain cancer cells resistant to irradiation and may increase after clinical course of therapy

WEDNESDAY, Dec. 20 (HealthDay News) -- A subset of breast cancer-initiating cells are resistant to radiotherapy and may increase after a short course of fractionated radiation, researchers report in the Dec. 20 issue of the Journal of the National Cancer Institute.

Frank Pajonk, M.D., Ph.D., of the David Geffen School of Medicine at the University of California Los Angeles, and colleagues exposed CD24-/low/CD44+ breast cancer-initiating cells and normal cells to single or multiple doses of radiation.

The investigators found that 46 percent of the cancer-initiating cells survived irradiation with 2 Gray of radiation, compared with 20 percent of normal breast cancer cells. Moreover, the proportion of cancer-initiating cells increased when they were treated with 3 Gy of radiation daily for five days. The researchers suggest that irradiation may activate the Notch-1 developmental pathway, which may have caused the number of stem cells to increase.

Despite several limitations, namely that the new study used tissue culture cells not tumors, the new findings "provide evidence that cancer stem cell-like cells may be intrinsically radioresistant, a finding that could clearly have important clinical implications," write Maximilian Diehn, M.D., Ph.D., and Michael F. Clarke, M.D., of the Stanford University School of Medicine in Stanford, Calif., in an editorial accompanying the study.

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