CA9 and neoplasm: Necrosis may be attributable to several factors (Mueller-Klieser et al, 1983; Parliament et al, 1997; Ramanujan et al, 2000), but an important factor is likely to be hypoxia and the relation between CA IX and necrosis is consistent with the recently described relation between HIF-1α and prognosis in tumours (Zhong et al, 1999).