Subsequent studies have shown that CAIX is expressed in only a few normal tissues (mainly the gastrointestinal tract), whereas it is ectopically induced under hypoxic conditions and highly overexpressed in many different cancer cell lines and tumour tissues, where ca9 is one of the most upregulated gene in a (HIF-1)-dependent manner (Wykoff et al, 2000). Here, HIF1A is linked to cancer.