Scientists estimate that as much as 17 percent of all cancers are caused by viruses, including the human papillomaviruses (HPVs) implicated in cervical and oral cancers. In the race to develop new and better cancer treatments, molecular biologists are delving into HPV's evolutionary tree to uncover the mechanisms of cancer causation. Their work is helping revolutionize patient treatment and is bringing new hope that virus-triggered cancers can be prevented.