CA9 and nonpapillary renal cell carcinoma: Additionally, elevated levels of carbonic anhydrase IX (CA‐IX) expression have been consistently observed in tissue samples of RCC patients with constitutive activation of hypoxia‐inducible factor (HIF).[14] In our study, a typical examination of a ccRCC patient's tumor tissue (Figure S9, Supporting Information) revealed a positive expression of CA‐IX.