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.
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“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.
Injecting the mice with an antibody that blocks TGF-beta averted the increase in lung tumors due to radiation therapy or chemotherapy, Biswas and her colleagues report. In another experiment, mice genetically engineered to have no response to TGF-beta also showed no increased metastasis, the team reports in the May Journal of Clinical Investigation. Blocking TGF-beta had no effect on the original tumor, however.
The researchers say that if future experiments show that TGF-beta influences tumors in people in a similar way, doctors should investigate therapies that combine cancer treatments with doses of TGF-beta antibodies.