The human colorectal and breast cancer cells exposed to Nar displayed a marked up-regulation in the mRNA expression of pro-apoptotic genes including Caspases-3, 7, 8, and 9, Bak, AIF and Bax. Meanwhile, the mRNA expression of the anti-apoptotic genes including Bcl2, x-IAP and c-IAP-2 was differentially down-regulated in both colorectal and breast cancer cells. This evidence concerns the gene CASP3 and breast cancer.