Radiation and chemotherapy can destroy a tumor, but they may also indirectly promote metastasis, the spread of cancerous cells to other organs.
Scientists knew that these traditional cancer therapies increase blood concentrations of a protein called transforming growth factor beta (TGF-beta), which performs many functions in a healthy individual. Now, researchers have shown that in mice with a form of breast cancer, TGF-beta promotes survival of stray tumor cells in the bloodstream, which in turn increases the number of new tumors in the lungs 17-fold.
"Nobody before has clearly pointed out the connection between TGF-beta and the increased metastases," says Swati Biswas of the Vanderbilt University School of Medicine in Nashville.
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