If it based on true goings on within the company for example a merger or an actual sale taking place, than there will be a large move up that may be sustainable if the sales prove to be sustainable or the merger actually takes place.
If there is pr that promises on something that can't be delivered or people pass off rumors as truth than the stock price will go up for a short period until the bag has been passed to the next bunch of "investors". The company could issue shares into the hype and the investors could be sitting on more diluted and near worthless shares in the not too distant future. And if they are lucky, a new pile of investors will be set up for the next bucket of news that comes out of the company.