Therefore, we chose the A549 cell line, which has an activating mutation in KRAS, and p53-deficient H1299 cells of NSCLC, H446, and H1688 cell lines of SCLC, which both contain p53 and PTEN mutations, to represent our in vitro model for lung cancer chemotherapy resistance study. The gene discussed is PTEN; the disease is small cell lung carcinoma.