Folkman hypothesized that large, primary tumors secrete an inhibitory substance to prevent blood vessel formation and the growth of the many smaller, secondary tumors that coexist in diseased individuals.

The critical point in O'Reilly's research came when he discovered that what inhibits the tumor growth is a collection of proteins produced by the body itself.

O'Reilly said that purifying the proteins was quite a chore.

"We had two hundred liters of mouse urine, collected by yours truly," he said.

O'Reilly explained that endostatin and angiostatin--a similar protein still being studied as well--both are part of larger complexes in the body.

Endostatin is part of the molecule collagen 18, while angiostatin is part of plasminogen, a blood clotting agent.

It is likely that these proteins lead a double life, mainly functioning in the large complexes but also naturally acting as cancer fighters.

"Most people have microscopic cancers in their bodies," O'Reilly said. "Autopsies of men who died of other causes reveal that 90 to 100 percent of them had cancers in their prostates."

It is possible that the inhibitor proteins function to control these small cancers in all individuals, and that their use in large doses could mimic the body's natural defenses, albeit on a larger scale.

Future research may enable scientists to turn on these cancer-fighting genes so the proteins are produced at high levels by the body. Without any pills, needles or chemotherapy, the body itself could produce weapons to fight the disease.

For now, O'Reilly pictures the drug as one piece of artillery in a larger arsenal that includes chemotherapy and other drugs.

Like Folkman, O'Reilly has a surgery background and does clinical work in addition to his research.

He said that the combination has been a factor in the success of the research.

"Every day I see people who need stuff like what I'm working on," O'Reilly said. "It really emphasizes why I'm doing the research.