Although overexpressed or recombinant caspase-6 was able to cleave CAD, the endogenous caspase-6 was not required for the 5-FU-induced CAD cleavage in GC and CRC cells, as the caspase-6 inhibitor, Z-VEID-FMK, did not block the 5-FU-induced CAD cleavage (lane 4 of Fig. 2g and Supplementary Fig. 2t). This evidence concerns the gene CASP6 and colorectal carcinoma.