CA9 and neoplasm: Monoclonal antibodies have also been used to achieve a selective in vivo localisation on cells, which display a high constitutive expression of CA IX (van Dijk et al, 1991; Chrastina et al, 2003a, 2003b; Brouwers et al, 2004; van Schaijk et al, 2005), especially kidney cancer cells, in which mutations in the gene encoding the von Hippel-Lindau tumour suppressor (pVHL) lead to a constitutive HIF-1α activation and, as a consequence, to a strong upregulation of CA IX on all tumour cells (Wykoff et al, 2000; Mazure et al, 2004).