Figure 4(a) also shows that bufalin promoted the active form of caspase-3 in a time-dependent manner, which also indicated that bufalin induced apoptosis of A375.S2 cells via caspase-dependent pathway. It is well documented that caspase is normally present as an inactive procaspase but it can exist as a cleaved form when triggered [41, 42]. Those observations are in agreement with other reports which showed that bufalin induced apoptosis in human hepatocellular carcinoma cells and human prostate cancer cells via Fas and FasL pathway and caspase pathways [17, 26]. This evidence concerns the gene CASP3 and prostate cancer.