As shown in Fig 3D, Bax, cleaved caspase-3, cleaved caspase-9, cytochrome C and cleaved PARP levels were increased after treatment with Rk3, whereas Bad and Bcl-2 levels were reduced in a dose-dependent manner in both Eca109 and KYSE150 cells, indicating that Rk3 activated apoptosis in esophageal cancer cells. This evidence concerns the gene CASP9 and esophageal cancer.