CA9 and neoplasm: Despite many debatable points, our present work seems to extend the current knowledge with several important findings: (i) CAIX is inducible and significantly increased by the neoadjuvant chemo-radiotherapy in rectal adenocarcinoma; (ii) failure in tumor response defined by TRG following neoadjuvant therapy is associated with high CAIX expression; (iii) the mutant KRAS status is associated with increased CAIX expression and their synergistic effects can be suspected in cancer progression and treatment failure.