Carbonic anhydrase IX (CA IX) protein (previously named as MN or MN/CA IX) is a cell membrane protein (Pastoreková et al, 1992; Závada et al, 1993), which is ectopically expressed in various human tumours, mostly carcinomas, for example, cervical, renal, colorectal, lung, mammary and others (Liao et al, 1994, 1997; Saarnio et al, 1998). Here, CA9 is linked to carcinoma.