CA9 and nonpapillary renal cell carcinoma: Another promising cancer target is carbonic anhydrase IX (CAIX), overexpressed in clear cell renal cell carcinoma (ccRCC) and other hypoxic tumors.[31, 32] However, selective targeting of CAIX is challenging due to its high homology with other carbonic anhydrases, which are expressed in normal tissues like the kidneys and stomach, limiting therapeutic applications.[31, 32, 33]