Microwave technology originally designed to shoot down nuclear missiles could help zap breast cancer tumors, according to a study that appeared in a recent issue of Annals of Surgical Oncology.

Researchers at the health sciences center of the University of Oklahoma in Oklahoma, City, Okla. used overlapping arrays of microwave beams to dramatically shrink tumor size in breast cancers, especially when used in combination with chemotherapy.

The study, conducted in two parts, tried to see how much microwave heat was needed to kill breast cancers and how effective it was at shrinking tumors when used in combination with chemotherapy.

Although microwaves have been used to treat some breast cancers for several decades, this is the first time a two-generator approach, borrowed from the Star Wars missile defense program, was harnessed against cancers.

In the technique, called focused microwave thermotherapy, a two-channel 915-MHz phased-array microwave system generates waves at very low wattage that deliver the greatest punch where they intersect, over the tumor.

The beams work on cancers exactly as your microwave at home works on your food, mainly by agitating molecules in water.

"It heats up by exciting the atoms just like it does in the microwave," William Dooley, M.D., a professor of surgery at Oklahoma and lead author of the study, tells DOTmed News.

The multiple-array technique lets doctors deliver low amounts of heat to healthy tissue but destructive amounts to cancers. The therapy is so deadly against cancers in part because the cancer heats up quicker than the healthy breast tissue.

"We're not 100 percent sure why breast tumor tissue heats up faster," says Dr. Dooley, "but there's more water in breast cancer than in the surrounding normal tissue." There's also more salt per volume in the tumor, and Dr. Dooley says salty foods heat up faster in the microwave. Plus, normal breast tissue is fatty, which acts as natural insulation. "It's almost like a Styrofoam cup," he says.

Tumors also take less heat to die. In one leg of the study, the doctors tested to see how much heat is required to completely eliminate a cancer, and found it took around 49 degree Celsius or more to exterminate it. Again, doctors aren't sure why tumors in the breast are more susceptible to heat than healthy tissue, but Dr. Dooley suggests it might be because the vessels that carry blood to tumors are more susceptible to clotting when they cool down.

Whatever, the case, when combined with cancer-killing drugs, the technique dramatically shrunk cancers. In the second leg of the study, ultrasound measurements showed that on average treatment with microwave heat plus chemotherapy reduced tumor size by nearly 89 percent, while cancer drugs alone only shrunk the tumors by around 59 percent.

And because the tumors' heat sensitivity makes them selectively affected by the treatment, the technique makes it easier to determine tumor margins. Scar tissue from the microwave heat naturally forms the borders of the areas that need to be removed during breast conservation surgeries.

"It biologically determines its own margins," says Dr. Dooley. "You don't have to artificially determine it with imaging."

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Although we colloquially say that microwaves "nuke" food, microwaves are not ionizing radiation and do not appear to pose any radiation-associated health risks. In microwave thermotherapy, the main side effects are pain near the surface of the skin from the heat or even small burns around the temperature probe used in the study to measure how much energy the tumor received. In clinical practice, these probes might not be needed, and the pain near the surface can be lessened by blowing cool air against the skin.

Dr. Dooley thinks microwave thermotherapy could be useful in shrinking tumors in other organs, such as the liver, which is solid and doesn't shift around a lot. But the real use for it could be to heat-activate drugs over cancer sites, so they deploy their toxic payload only over the tumor and not expose the rest of the body to harsh, cell-destroying medication.

For now, Dr. Dooley hopes to launch another round of studies, recruiting several thousand patients from multiple centers around the world, to see if the technique can work against larger tumors.

"First, [we need to] demonstrate in the redesign that equipment for larger tumors [can] down-stage those tumors with fewer doses of chemotherapy and get the same or greater effects," he says.

He would also hope by biopsying the cancers to at last truly figure out exactly how the microwaves are heat-killing them.

"That would be one of the components of a clinical trial, taking tumor samples," he says. "Although it's been observed for 30 years, no one has come up with the plausible, testable hypothesis that's convincing. It's something we need to understand better."