AREG and cancer: This study has several limitations: first, this study is a retrospective observation examine and the gastric tissues of patients were obtained from 2003 to 2010, the conclusion might not be suitable for the current population; second, IHC used in this study is a semiquantitative method, additional study in vivo and in vitro should be done in the future to confirm the role of Trop2 and AREG in cancer cells; Third, the number of genes coexamined in this study were relatively small and other useful candidate genes should be studied.