Since these observations suggest the presence of an inhibitor of caspase-9 activity in lung cancer cells, and based on the reported binding of TUCAN to procaspase-9 via their CARD motifs leading to caspase-9 inactivation [11], a possible role of TUCAN in blocking caspase-9-mediated apoptosis in lung cancer cells was explored. This evidence concerns the gene CASP9 and lung cancer.