Chicago, shorting Isis isn't suicidal at all! That is a fallacy, just like people thinking that market makers determine where a stock is going to move. They don't! It is the guy that buys on the ask and sells on the bid that moves a stock like Isis. The guy that is willing to pay an extra 2 cents a round trip, all else being equal, is in control.
Don't forget that you are only going short after all the good news has been priced into the stock. The trader caught without inventory on an announcement can simply wait to the open, see which way the wind is blowing, then pile on short or long. If the stock goes up he goes long until he sees it falter, then quickly reverses and starts selling his previously acquired position and goes short the market, follows it down, waits for the first wave of selling, covers and goes long again. He rides it back up and when it falters again, sells again and shorts the stock, again at the market and rides it down. Don't forget you are holding only for minutes or seconds at a time, so all of the risk that you are dealing with is pure market risk. Long term holders have many risk factors to deal with but not the day trader! Don't forget that the way I am speaking of risk, it can be both a positive and a negative event (ISO 31000).
Have you ever heard the phrase, "buy the rumor, sell the news"? Traders who come into the "news driven trading event" with inventory have to worry about a sell off at the open as well as anticipating a gap up at the open. This places a burden on their trading activity. Don't forget that with the Mipo event, everyone knows it is coming and most individuals anticipate a positive result. Much of the news may well be priced into the stock already and there is risk that the news will be a non-event, with no positive price movement. That has been the norm for Isis lately, news does nothing for the price. Since nobody knows where Isis will head on "announcement day", holding inventory may be no advantage at all!!!!!!
I would say the reason to hold now, is not the anticipation of a gap up on announcement, but anticipation of a ramp up in share value as we approach announcement. That would be the norm with a biotech, but it does not seem to be happening with Isis at this time, If the announcement goes like all other Isis news has gone lately, there will be a sell off after the announcement and only the shorts will benefit from "news". It is hard saying what is going to happen in this situation, but it is always safer, if not as profitable, going into these events with a lean inventory!!!
Darkster, if you read this, remember, the nation appreciates all veteran's efforts to make America a safe and secure democratic republic! That was a difficult time period for America and those who served!