I'm not sure, but once it closes above $5 it becomes marginable unless the individual firm(i.e. Schwab) restricts it's purchase on margin. If anybody knows for sure please speak up. Of course, it cuts both ways as once it is marginable the shorts can short more.
Let them short away. You can't stop EXEL, as they do not need cash, and CABO is owned 100%. There is no leverage for shorts. So they short and time rolls on CABO rolls out and gets further approval and off label use. Any hint of a bid to take over, merger, partnerships, news on other projects, or just the unfolding story and they create their own problem and make longs a bigger win quicker. Any look at the long term charts screams buy. Whether TA, Fundamentals or speculation on unfolding future, this stock says accumulation and far higher price all through 2013 and beyond. If some are stupid enough to be actually short here now. Its their problem and longs friend. I have repeatedly advised: forget short term stuff unless you like to play and trade, otherwise all you have had to do is accumulate a position as they hand you a gift, and wait a bit. Its called investing, by the way! LOL