Localized radiation therapy for breast cancer kills cancer cells at the tumor site. But, in a cruel irony, Stanford radiation oncologist Edward Graves, PhD, and research associate Marta Vilalta, PhD, have found that the dying cells in the breast may send out a signal that recruits other cancer cells back to the site of the initial tumor. Their work was published today in Cell Reports. As Graves explained in an e-mail to me:
Cancer spreads by shedding tumor cells into the circulation, where they can travel to distant organs and form secondary lesions. We've demonstrated with this study that cancer radiation therapy may actually attract these circulating tumor cells, or CTCs, back to the primary tumor, which may lead to the regrowth of the tumor after radiation therapy.
The researchers studied mouse and human breast cancer cells growing in a laboratory dish, as well as human breast cancer cells implanted into mice. They found that irradiated cells secreted a molecule called granulocyte macrophage colony stimulating factor, or GM-CSF. Blocking the expression of GM-CSF by the cells inhibited (but didn't completely block) their ability to recruit other cells to the cancer site. The finding is particularly interesting, since physicians sometimes give cancer patients injections of GM-CSF to enhance the growth of infection-fighting white blood cells that can be damaged during chemotherapy. As Graves explained, "This work has important implications for clinical radiotherapy, and for the use of GM-CSF in treating neutropenia in cancer patients during therapy."
The researchers say, however, that cancer patients shouldn't eschew radiation therapy. Rather, the finding may help clinicians devise better ways to fight the disease - perhaps by blocking GM-CSF signaling. Graves concluded:
It should be emphasized that radiation therapy remains one of the most effective treatments for cancer. Our findings will help us to further optimize patient outcomes following this already potent therapy.
Previously: Using 3-D technology to screen for breast cancer, Blood will tell: In Stanford study, tiny bits of circulating tumor DNA betray hidden cancers and Common drug class targets breast cancer stem cells, may benefit more patients, says study