CA9 and nonpapillary renal cell carcinoma: Furthermore, CA9 is also highly expressed in a large proportion of clear cell Renal Cell Carcinoma (ccRCC) (32) in a hypoxia-independent manner where it is driven by stabilization and constitutive activation of HIF-1alpha signaling as a result of mutation of the von Hippel-Lindau (VHL) tumor suppressor (33, 34).