Heating breast-cancer cells with focused beams of microwave energy after chemotherapy can significantly shrink and kill tumors, according to results from a new clinical trial. The treatment increases blood flow into tumors, allowing chemotherapy drugs to more easily invade cancer cells. In patients who received both the heat treatment, known as thermotherapy, and chemotherapy, tumors showed 50 percent more shrinkage than tumors that strictly received chemotherapy, allowing the majority of patients to avoid mastectomy.

“In part, we are killing the cancer cells with heat, and we are also making the chemotherapy drug more effective by increasing blood flow to tumors that typically have poor vasculature,” says Alan J. Fenn, a senior staff member at the Lincoln Laboratory at MIT, who originally developed the technology. The technique is similar to the idea of radiation therapy but with fewer side effects. “Radiation therapy blankets the entire breast, and what we are trying to do is heat cancer cells in a large region of the breast to kill them,” says Fenn.

Previous studies of Fenn’s thermotherapy showed that it could shrink small to large tumors. In the newest study, published online last week in the journal Cancer Therapy, researchers aimed to use the microwave treatment in combination with chemotherapy to shrink tumors enough to allow patients to undergo lumpectomy–breast-conserving surgery–rather than radical mastectomy, or removal of the breast.

Fifteen of 28 patients received two cycles of chemotherapy, followed a few hours later by thermotherapy, in which a 915-megahertz microwave was focused on the tumor, raising its temperature to 108 ºF. After the combined treatments, 14 of the patients’ tumors decreased enough for lumpectomy: the volume of the tumor shrank by about 88 percent, compared with 59 percent in patients who received chemotherapy alone. The trials were conducted at UCLA Medical Center, in Torrance, CA; the University of Oklahoma Health Science Center, in Oklahoma City, OK; the Comprehensive Breast Center, in Coral Springs, FL; and St. Joseph’s Hospital, in Orange County, CA.

There are minimal treatment options for patients with tumors deep in the breast or with large tumors in the intact breast, says Paul Stauffer, a professor and director of hyperthermia physics in the radiation oncology department at Duke University Medical Center, in Durham, NC. “Based on the results of the trial, this may be the best approach to treat tumors in the intact breast,” he says.

The microwave technology used in the trial was originally developed at MIT as a missile-detection tool. (See “Microwave Tumors.”) Two plastic plates, one placed on either side, gently compress the breast, while microwave antennae about an inch away from the plates deliver the microwaves, preferentially targeting the high water and high ion content of the breast-cancer cells rather than the low water and low ion content of the healthy, fatty tissues. The antennae adaptively focus the microwaves at the tumor position. The energy sent through the tumor causes the water molecules to collide and generate heat through friction, eventually elevating the temperature of the tumor.

“This is a very promising future direction for breast-cancer treatment, and hopefully for other tumors as well,” says Constance D. Lehman, a professor and the vice chair of radiology at the University of Washington, and the director of radiology at the Seattle Cancer Care Alliance.

To date, about 100 patients have received the focused microwave treatment in four clinical trials. The team of researchers is now preparing for a larger clinical trial, estimated at 228 patients, to start in 2008. Fenn says that it will take about two years from the time the researchers start the study for the technology to be approved by the Federal Drug Administration.