Given the importance of triggering apoptosis for butyrate to exert its anti-cancer effects [23], we did related investigations and found that butyrate significantly increased Caspase 9 but not Caspase 8 or 12, accompanied by elevated expression of Apaf-1 and Cytc, indicating activated mitochondria-dependent apoptosis, which is consistent with the findings by Tiwari et al. [24] in skin cancer. Here, CASP9 is linked to skin cancer.