CA9 and cancer: In hypoxic tumours, CAIX activity contributes to the maintenance of a pHi favorable for cancer cell survival and growth, and simultaneously facilitates acidification of the TME, thereby promoting tumour cell invasion and metastasis, as well as immunosuppression and therapeutic resistance (McDonald et al., 2012; Boyd et al., 2017; Chafe et al., 2019; Pastorekova and Gillies, 2019).