The following novel findings were demonstrated in our current study: (1) higher IGF-1r expression was observed in human TE-1 cells than in Eca-109 cells; (2) effective inhibition of cell proliferation and apoptosis in the presence of IGF-1r siRNA following radiotherapy was demonstrated in vitro; and (3) enhancement of tumor growth radiation sensitivity after IGF-1r siRNA treatment was observed in vivo. Thus, we demonstrated that greater therapeutic efficacy may be obtained by enhancing the sensitivity of tumors to radiotherapy in the presence of IGF-1r siRNA knockdown. The gene discussed is IGF1R; the disease is neoplasm.