Whilst pre-clinical and early clinical studies have shown strong correlations between CAIX expression and tumor hypoxia (assessed by both Eppendorf pO2 probe measurements and the exogenous hypoxia tracer pimonidazole) [6], [15], [16], the general usefulness of CAIX as an endogenous marker of tumor hypoxia remains to be fully established. Here, CA9 is linked to neoplasm.