Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of Medivation (Nasdaq: MDVN) have more than doubled today, up by as much as an astronomical 135%, after the company announced its prostate cancer drug has proven effective.

So what: The biotech company announced that a phase 3 clinical trial showed that its drug candidate MDV3100 successfully met the study's pre-specified interim efficacy stopping criteria. The drug demonstrated a clinically meaningful and statistically significant improvement in overall survival compared to placebo.

Now what: MDV3100 showed a median overall survival advantage of 4.8 months and provided a 37% reduction in risk of death. Medivation is looking to meet with U.S. regulators early next year to discuss filing for regulatory approval, with analysts expecting approval in early 2013 that could promise annual revenue north of $1 billion. The news is also contributing to a sharp sell-off in rival Dendreon (Nasdaq: DNDN), which offers prostate cancer drug Provenge that has been facing sales headwinds.

Interested in more info on Medivation? Add it to your watchlist by clicking here.