One day, Medivation shares are up 9% for the year. Twenty-four hours later, Medivation is up 162%. This sudden and spectacular jump in market value -- akin to winning the lottery -- is what makes biotech stocks irresistible for so many investors. Medivation's spark was the November announcement of a successful phase III study for its prostate cancer drug MDV3100. The stock: Medivation shares weren't done moving higher after that very good, early November day. As of Dec. 16, Medivation is up 199% for the year.