It's a good start when experimental compounds stop the proliferation of cancer cells in the lab. But, as many researchers have learned the hard way, that's just an early step toward creating a worthwhile treatment. Science Source hide caption

itoggle caption Science Source

If you're interested in buying Viagra, Pfizer, the drug's maker, will now sell it to you from its official website. William Vazquez/AP hide caption

itoggle caption William Vazquez/AP

A PET scan of the brain of a person with Alzheimer's disease. U.S. National Institute on Aging/via Wikimedia Commons hide caption

itoggle caption U.S. National Institute on Aging/via Wikimedia Commons