WASHINGTON, Nov. 13 -- Tiny nanoparticles could be launched into tumors and heated up using near-infrared light to destroy cancer cells, says a group of Texas researchers who have experimented with the technique on mouse tumors. Writing in the Proceedings of the National Academy of Sciences, the researchers said cancerous tissue was destroyed and healthy tissue was spared using the technique. The "nanoshells" -- so small it would take 5,000 of them to reach the size of a poppy seed -- are made from silica coated with gold, which would be injected into a tumor located using a scanner. A near-infrared wavelength light would then be shone on the area. This penetrates the skin to reach the tumor, and, at the right frequency, actually causes the particles to heat up. Enough heat is generated to damage the cancer cells and ideally restrict the growth of the tumor, but surrounding cells would be undamaged. The work is at an early stage, but animal experiments have encouraged the researchers. They injected mouse tumors with the nanoshells, and within four to six minutes the near-infrared light heated them up enough to kill the cancer cells. The team suggested that, in time, the technique could have a "large impact" on treatment. Nanoshells should work in most soft tissue tumors but would be most effective on cancers that can't be removed surgically because they're in an awkward location, such as in the brain, the researchers said. "Nanoshells can be directly injected," said Jennifer L. West of Rice University in a BBC report. "Or, our most recent study shows that you can inject nanoshells intravenously and they will accumulate in tumor sites because the blood vessels in tumors are leakier than elsewhere in the body." Patients could be treated in two ways: Near-infrared light can be applied from outside of the body for most applications, but if necessary, fiber optics can be run through catheters, said West, who led the team from Rice and the University of Texas M.D. Anderson Cancer Center. The team first experimented with cultured human breast cancer cells in a solution containing nanoshells, then tried them out on tumors in mice. In both cases, temperatures inside the tumors reached levels high enough to damage cells within 4 to 6 minutes, killing the tumors but leaving surrounding tissue unharmed. The researchers will monitor the long-term health of the treated mice. West said a Houston company, Nanospectra Biosciences, has licensed the technology and plans to do studies in people in the next year or two. For more information, visit: www.pnas.org