SAN FRANCISCO ( TheStreet) -- Medivation ( MDVN) and its partner Astellas will soon announce results from a phase III study of the prostate cancer drug Xtandi. This is a very important study for Medivation because a positive outcome is likely to transform Xtandi into a blockbuster cancer drug. As you might expect, Wall Street is paying close attention, waiting anxiously for the companies to announce results. Here's an FAQ on what to expect from the Xtandi study, known as PREVAIL: Xtandi is already approved to treat prostate cancer, so remind me why this PREVAIL study is important? You're right, the FDA approved Xtandi in August 2012 to treat men with advanced prostate cancer, specifically those with cancer that no longer responds to chemotherapy. If you want to be hip to the lingo, these are "post chemo" prostate cancer patients. The PREVAIL study is being conducted in "pre chemo" prostate cancer patients. These men have less advanced disease and have not yet been treated with chemotherapy. Less advanced prostate cancer means more patients to treat and a more lucrative commercial market opportunity for Medivation and Astellas? Bingo. Medivation has guided to 2013 Xtandi sales in the range of $345-365 million, based only on treating post-chemo prostate cancer patients. If the PREVAIL study is positive and Xtandi wins an expanded FDA approval for pre-chemo prostate cancer, Xtandi sales are likely to be on a billion-dollar run rate by the end of 2014. Peak sales in prostate cancer could be in the $3 billion range. The drug is also being studied in breast cancer. Medivation's market value already tops $4.3 billion, so.... Yeah, I get what you're saying. Substantial, future Xtandi sales are baked into Medivation's stock price already. How much, exactly, is hard to say. This doesn't mean Medivation shares won't move higher on positive PREVAIL results, but investor expectations are high. Alright Adam, what do your hedge fund investor buddies want to see from the PREVAIL study to make them happy about Medivation? Here we go. For starters, it's easiest to think about Xtandi relative to its major prostate cancer competitor, which is Johnson & Johnson's ( JNJ) Zytiga. Zytiga is already approved for pre-chemo prostate cancer based on data from a phase III study which demonstrated a five-month median survival benefit (Zytiga 35.3 months vs. 30.1 months for placebo) and an overall survival hazard ratio of 0.79. That's your basic comparison for Xtandi in the PREVAIL study. Whoa! Slow down, sport. What the heck is a hazard ratio? Oops, sorry. I got lost in jargon. Let's step back a moment. Median overall survival, expressed in weeks or months, is relatively easy to understand. Median means middle, so in cancer drug studies, median overall survival is the length of time that half the patients are still alive.