The idea of heating a tumor to make it more vulnerable to radiation treatment has had appeal for decades. But tests in the early 1990s yielded negative or inconsistent results. In Europe, the methods for this tricky procedure have improved since then and test results have shown promise. Still, the combination of procedures has been used sparingly in the United States.
In a new U.S. study, researchers have demonstrated that when tumors were kept warmer than 40°C for at least an hour after radiation treatment, they shrank significantly more than did irradiated tumors that weren’t heated.
Scientists at Duke University Medical Center in Durham, N.C., identified 109 patients who had at least one tumor within 3 centimeters of the skin surface. Most were patients whose breast cancer had recurred after surgery. Other participants had melanoma or head-and-neck cancer that had spread. All the volunteers were scheduled to receive radiation for at least one tumor, deemed inoperable, that had invaded the chest wall.
Doctors randomly assigned the patients to get radiation and heat or radiation alone. The patients received the therapy once or twice a week for up to 10 treatments. At each combination-therapy session, the scientists first applied radiation and then heated the target tumor to between 40°C and 43°C. They monitored the temperature throughout each tumor with fiber-optic thermometers.
Treatment destroyed the tumor in 66 percent of patients getting radiation and heat but in only 42 percent of those getting just radiation, says Ellen L. Jones of Duke.
In both groups, patients who had previously undergone radiation therapy received, on average, lower doses of radiation than the others did. The tumor was demolished in 15 of the 22 low-dose patients who received the heat treatment. In contrast, only 4 of 17 low-dose patients not getting heat showed such progress, the researchers report in the May Journal of Clinical Oncology.
Past research has shown that heat kills some cancer cells directly. Moreover, after radiation damages DNA in a tumor cell, heat prevents enzymes from repairing the DNA, and the cell dies, says study coauthor Mark W. Dewhirst.
The Food and Drug Administration has approved heat use in conjunction with radiation as a cancer treatment, but few doctors are trained to use it, says Dewhirst.
Michael J. Borrelli of the University of Arkansas for Medical Sciences in Little Rock says that heat treatment, or hyperthermia, for cancer is practiced much more in Europe and the Far East than in the United States. Because of the early failures, “there is a stigma in this country against hyperthermia,” he says.
“This [new] study is well designed, and the findings are sound,” Borrelli says. This technique might someday be applied to deep tumors as well, he says.