The HCT116 CA9 colorectal tumours uniformly expressing high levels of CAIX protein, along with their EV counterparts in which CAIX is induced only in hypoxic regions, offer a tractable experimental platform to study the effect of CAIX expression on tumour pHe in vivo, independent of changes in tumour vascularity, oxygenation and metabolism. Here, CA9 is linked to colorectal neoplasm.