In 2010 came word that Stallone was developing a fifth "Rambo" movie using James Byron Huggins' novel "Hunter" as the template. While "Rambo" is done and dusted for Sly, "Hunter" doesn't seem to be out of his system as yet.
The story revolves around a veteran tracker being called in to a military project near the Arctic Circle. Seems a terrifying predator spawned by secret experiments has escaped and is headed south toward civilisation. He must find it and stop it.
The article claims Stallone is in talks with Lionsgate to get the movie out and on the screen by 2014. However there's no quotes or source confirming anything about it or any additional information. Consider it all speculative for now.