Medical research typically is a cautious, restrained affair—but every once in a while, scientists try out a radical idea. Take this one for example: injecting a live virus into someone with cancer on the off chance that the virus might go ahead and kill some cancer cells. Nuts? Actually this approach, called viral oncolysis, has been around since at least the 1950s, when West Nile virus, thought harmless at the time, was injected into people with an array of advanced and seemingly hopeless cancers. Some got a little better, some a little worse, but the approach fell away, eclipsed by...