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. This evidence concerns the gene KRAS and cancer.