Cancer surgery is currently "a guessing game," admits Bernard Lee, a surgeon at Beth Israel Deaconess. To identify tumor borders, surgeons rely on their own senses (cancerous tissue looks and feels different from healthy tissue) and on medical scans taken before the surgery. Surgeons can send tissue samples to the pathology lab during surgery for a quick examination, but a proper analysis takes between five and seven days. So the best strategy is often to cut a broad margin around the tumor, sacrificing some healthy tissue in the process.

Frangioni's imaging system is the first to allow real-time imaging of this kind in the operating room, says Lee, who has used it to distinguish between blood vessels and other tissue during experimental surgery on animals.

Near-infrared light can also penetrate through a few millimeters of tissue, allowing surgeons to see different layers. "It gives you the ability to see things that would otherwise be invisible," says Frangioni.

Other researchers are working on making cancer cells visible during surgery, and targeted fluorescent proteins similar to Frangioni's have helped surgeons achieve increased survival rates in other animal studies involving tumor removal. But the imaging systems used show a tumor only as a white spot on a black background. It's difficult for a surgeon to relate this to the real anatomy, says Lee: "You get a black-and-white, low-resolution image, and you can't tell where the [tumor] is in relation to the rest of the surgical field."

Frangioni's lab is also testing a less toxic fluorescent protein in animals. It is surrounded by biofriendly polymers but can still be attached to different types of targeting molecules.

James Olson, an oncologist at the Fred Hutchinson Cancer Research Center in Seattle, says fluorescent imaging agents have shown great promise in animal testing, but he notes that none has yet entered clinical trials in the United States. Frangioni believes that a good imaging system, integrated into surgical practice, will help research on fluorescent agents progress further.