On the basis of previous investigation, it has been validated that TRF2 promotes MDR of gastric cancer cells by interfering the activation of ATM-dependent DNA damage response.7 To further investigate how Rap1 affect TRF2-mediated resistance to etoposide in gastric cancer cells, overexpression of TRF2 in SGC7901 was firstly obtained after transfected with TRF2 eukaryotic expression vector. This evidence concerns the gene ATM and gastric cancer.