CA9 and neoplasm: Given the correlation of CAXII activity with tumor proliferation, invasion and chemoresistance, the interest in developing selective inhibitors of CAXII has increased in recent years, however in vitro and in vivo studies with small molecule CAXII inhibitors that directly link the mechanism of action to CAXII inhibition remain scarce and CAXII is much less studied than the other cancer-associated CA, CAIX.