In our previous study, 8 markers (P53, ETHE1, CTAG1A, C1QTNF1, TEX264, CLDN2, NSG1, and HRAS) which were enriched in the serum of lung cancer patients were identified (16), among them, 3 markers (P53, ETHE1 and HRAS) were proved to own strongly predictive ability in distinguishing healthy population (including parts of LBLs) and stage I~II lung cancer patients. This evidence concerns the gene CLDN2 and lung cancer.