In early February, Melissa Dauvalt noticed that her St. Bernard, Juno, had a lump on one of his front legs that was causing him to limp. Tests confirmed that the dog had developed osteosarcoma, an aggressive and difficult-to-treat bone tumor that's found most commonly in adolescent children and large-breed dogs. Dauvalt is a veterinarian, so she knew the most effective treatment would be amputation. But she couldn't bear the thought of her 165-pound canine trying to walk on three legs. "He's a big guy," says Dauvalt. "Amputation was not an option."

So Dauvalt and volunteered her dog for a clinical trial at Texas A&M University, where veterinarians are testing a new technology that delivers radiation directly to solid bone tumors. During a two-hour procedure on March 12, the vets used a drill roughly the size of an electric toothbrush to inject a radioactive isotope directly into the tumor, in the hopes of shrinking it without harming surrounding tissue. The lessons they learn from Juno's experience--and that of other dogs in the trial--will help scientists determine if such highly targeted radiation treatments could also work in humans.

Osteosarcoma afflicts about 900 people per year in the United States, about half of whom are younger than 20, according to the American Cancer Society. Some tumors can be removed effectively, but what makes the disease so devastating is its tendency to spread: One in four newly diagnosed cases have already metastasized, and the long-term survival rate is under 25 percent, says Crystal Mackall, chief of the pediatric oncology unit of the National Cancer Institute.

Osteosarcoma is genetically similar in dogs and humans, making the veterinary setting an important laboratory for researching human therapies. "Dogs develop cancer naturally, and they share our environment," says Melissa Paoloni, a scientist at the NCI's Comparative Oncology Program. That provides an opportunity to try potential new treatments in something other than rodents, which have to be engineered to develop cancer and therefore may not most accurately reflect the human experience. About 6,000 new cases of canine osteosarcoma are diagnosed each year, according to the National Canine Cancer Foundation.

The drill was the brainchild of Stan Stearns, founder and president of Valco Instruments, a Houston-based maker of medical devices. Stearns lost his St. Bernard, Gabriel, to osteosarcoma in 2008. During the yearlong effort to save Gabriel's life, Stearns learned that external-beam radiation--the type commonly used to treat cancer--wasn't really effective for bone tumors, and presented too much of a risk to surrounding healthy tissues. But after reading about experiments using biopsy tools to deliver medicine directly to bone, he had an epiphany. "Valco had developed tubing that I thought could be the basis of a drill that would be flexible enough to go around corners," burrow into bone, and deliver radiation directly to tumors, Stearns says.