Remember that the data for FDA decisions are almost always known in advance, so pre-decision stock activity is more likely investors/traders playing the event, not a leak.
The release of clinical trial results isn't usually scheduled in advance, so big stock moves here can signal a leak. Or not. Don't forget that professional biotech investors spend a lot of time talking to management and/or other experts seeking a more refined timeline for when data may be released. They may use this information or insight, which is not illegal, to guess better than the average retail investor.
In other words, Wall Street is not a level playing field. Professionals have more tools at their disposal than amateurs. That might not be fair, but it's just the way it is.
The best way for an investor to protect himself from leaks is to be on the right side of the drug-approval decision or clinical trial-data release in the first place. That way, either the leak works in your favor, or if the leak is wrong, you still win when the truth comes out.Leaks are bad. They're illegal. But leaks are also a part of Wall Street that will never go away, and I don't know what the SEC can do to change that.