Investigating carcinomas with proximal nephrogenicdifferentiation, particularly those exhibiting tubulardevelopment, may be aided by CA IX. A glycoprotein ofaround 200 kDa, known as the transmembrane proteinCarbonic Anhydrase IX (gp200), is recognised by Genebio’sCA IX antibody. This protein is increased in hypoxicconditions, such as necrosis. In a healthy kidney, CA IX isfound focally along the luminal surface of Bowman’scapsule, which is next to the outgoing proximal tubule, andalong the brush boundary of the pars convoluta and parsrecta portions of the proximal tubule. 84% of metastaticrenal cell carcinomas and 93% of basic renal cellcarcinomas express CA IX. CA IX has high membranousstaining in mesothelioma, mesothelial lesions, andmesothelium and is mostly used to differentiate kidneytumours, albeit it is not specific to renal primary tumours.