 Patients also undergo tissue sample collection at the time of nephrectomy. Tissue samples are examined by microarray analysis and IHC staining for expression of CD31PECAM, HIF1α, and HIF2α. Immunohistochemical staining to identify biomarkers of microvessel density is also performed. Tissue samples are also examined for gene expression and metabolic profile by small molecule mass spectroscopy, as well as VHL gene mutation by VHL mutation analysis. 