SAN FRANCISCO ( TheStreet) -- Stock-moving biotech events don't come any bigger or potentially more volatile than what lays ahead for Medivation ( MDVN) and its experimental Alzheimer's disease drug Dimebon.Medivation is gearing up to announce results from a phase III study of Dimebon which, if positive, could send the company's stock price soaring to $65 to $75 a share. Call it a double from the stock's Wednesday close of $33.12. If the Dimebon study fails, look out below. Medivation's stock price will plunge. Where it stops is anyone's guess, but let's says $10-$15 a share -- or a painful 50% scalping from its current price. The volatility expected in Medivation's stock price is scary and exciting at the same time. It's what biotech investors live for -- and dread. To prepare for the big event, I've put together a discussion of issues surrounding Dimebon, Alzheimer's and the upcoming phase III study results. The most important question first: When should we expect the Dimebon data to be announced? Medivation says the announcement should come in the first half of the year, but won't be any more specific. I think a more precise guess is likely March or April, given that the last patients enrolled in the Dimebon study completed the mandatory six months of treatment in December. Why is so much riding on this Dimebon study? One word: Alzheimer's. About 5 million Americans suffer from progressive neuro-degenerative disease today, 30 million worldwide, and the number is expected to triple by 2050. Current Alzheimer's drugs are only moderately effective but they still bring in about $5 billion in sales annually. If the Dimebon study is positive and leads to the drug's approval, sales could easily top $1 billion and possibly much more.