The results of this study demonstrate that type I and III ROP16 significantly induce apoptosis and cell cycle arrest in A549 lung adenocarcinoma cells by regulating cell cycle-related proteins (such as p21, CDK6, and Cyclin D1) as well as apoptosis-related proteins (including Bax, BCL-2, p53, and Caspase-9). This evidence concerns the gene CASP9 and lung adenocarcinoma.