Frank McCormick was flying home from a meeting on cancer genetics when a wild idea popped into his head. What if you could make a virus that would infect--and kill--cancer cells but leave healthy cells intact? The next day, McCormick excitedly explained his notion to colleagues at Onyx Pharmaceuticals in Richmond, Calif., a biotech company he had founded earlier that year. Some of them were as enthusiastic as he was. Others told him he was crazy; such a treatment couldn't possibly work.
Nine years later, McCormick, now director of the Comprehensive Cancer Center at the University of California, San Francisco,...