Morales et al (2005) recently confirmed these results, by showing that intracellular glutathione levels determine cell sensitivity to drug-induced apoptosis. It has also been demonstrated that intracellular GSH depletion of human oral squamous cell carcinoma by inorganic selenium compounds may cause caspase-9-mediated apoptosis (Takahashi et al, 2005). This evidence concerns the gene CASP9 and oral cavity squamous cell carcinoma.