On August 13th 2010, GSC Gameworld announced that a full fledged sequel to S.T.A.L.K.E.R. : Shadow of Chernobyl is in the works and was slated to be released in 2012. Billed as "the next chapter" in the series by CEO Sergiy Grygorovych the game will be using a new multi-platform engine that is being built from the ground up by the design team. No other details were given at the time of the announcement. The engine used to make the game was an updated version of X-Ray.
On December 9th it was reported on UkraNews that GSC Game World would be closing down. The unofficial reason for this is that Sergei Grigorovich founder and CEO of the company is unhappy with the development progress of S.T.A.L.K.E.R. 2.
The claim was later refuted on the developer's official twitter page, but that response was later taken down. Again, on the official twitter page, it's simply said "We will do our best to continue. However, at this moment, nothing is certain."
On April 25th, 2012 S.T.A.L.K.E.R. 2 was confirmed cancelled on the developers official Facebook page: link