Purpose: To investigate the mechanism of pretreatment with EGFR inhibitors sensitizes cancer cells to DNA-damaging therapy.Implementation &Methodology: MTT assay was applyed to detect inhibition of cell proliferation by EGFR inhibitors and Doxocubicin alone or in combination.Plasmids,siRNA were established by molecular cloning and lipofectamine transfection technology.Western blot analysis was used to detect the protein levels.Native-page was used to detect the formation of dimer.Immunoprecipitation was employed to determine the protein-protein interactions.Results &Conclusion: In this work, we found that pretreatment with EGFR inhibitors mediated caspase-8 homodimerization ,which sensitizes cancer cells to DNA-damaging therapy.ERK plays an important role in sequential application of anticancer drugs.P-ERK can phosphorylate caspase-8 at its S387 residue.Phosphorylation occurs at S387 results in reduction of caspase-8 homodimer ,followed by down-regulation of caspase-8 proapoptotic fucntion.Non-phosphorylatable(S387A) caspase-8 significantly enhanced doxorubicin-induced cell death.The relevance of ERK in response and resistance to antitumor agents has been recognized, ERK can act in protective signalling pathways, thereby limiting DNA damage.Silence of ERK by siRNA can sensitive breast cancer cells to doxorubicin.DNA-damaging therapy leads to the activation of ERK and pretreatment with EGFR inhibitor or MEK inhibitor can eliminate this protective effects by ERK,while coadministration of these two kind ofanticancer drugs does not.In conclusion, our studies identified ERK as a key participator in the mechanisms of sequential application of EGFR inhibitor and Doxorubicin.Pretreatment with EGFR inhibitor promotes caspase-8 homodimer that leads cancer cell in apoptotic status.Our findings may provide a new strategy for combinational therapy.