You have to understand that GENT was trading on it's fundamentals (I know I sound like a broken record with the fundamentals thing). When something or some event changes those fundamentals a stock will trade in line with them over time. That's how Wall Street and investing works. However, for most stocks it takes a little time for the PPS to catch up with those "New" and better fundamentals, with a stock like GENT and it's very low float, the process isn't as slow than say a stock like Citi group with billions and billions of shares. Why do you think a stock goes down on bad guidence? The PPS is changing with it's fundamentals.
Gent announced last week they were going to be cash flow positive for the rest of this year into 2011, and they also said they had enough cash for all of 2010 into 2011. A bio tech with no earnings, a few good products in the pipeline, and being cash flow positive is a very rare thing and very very positive...hence the share price rising...with such a low float, the process of share price being in line with fundies is just sped up a bit more..