CA9 and neoplasm: The results showed that the skrc-59 CAIX+ tumor cell line used in our research [17, 19–21] recapitulates CAIX expression levels on ccRCC patient tissue, while both sgCAIX skrc-59 tumor cells, that were engineered to knock out CAIX using CRISPR/Cas9 and single guided RNA (sgRNA) targeting CAIX, and MMNK-1 cholangiocyte [22] cells represent a similar CAIX density as observed in bile duct (Fig. 1D).