In the currently ongoing retrospective aspect of the study, we will obtain pathologic tumor explant specimens from the tumor explant population from 8/1/1994 to 12/31/2005. We will prepare 5-10 slides from each tumor explant block and measure HIF-1α using immunohistochemical staining. We will also be performing a retrospective chart review for specific data points which we believe are needed to assist us in our analysis of the histopathologic specimens.