Greg just tweeted a blog post that he was diagnosed with Hodgkin's lymphoma. It's up at http://www.ign.com/blogs/greggy-ign/2012/08/09/so-i-have-cancer-who-wants-to-cook-meth/ (that links to his myIGN blog post). The prognosis is very good, but it's still a rough thing to go through.
I wish him the best. Fight it, man.
(edited with the actual links, updated some text)