Abstract: Objective : To investigate the therapeutic potential of amphiregulin mRNA antisense delivered by adenoviral vector in a human breast cancer model. Methods : Human amphiregulin cDNA was subcloned in the opposite orientation to the cytomegaloviral promoter and inserted into a E1/E3-deleted type 5 adenoviral vector to obtain AdA4 construct which expresses amphiregulin antisense mRNA. Both in vitro and in vivo antiproliferative effects of the antisense mRNA were studied by infecting transformed human breast epithelial NS2T2A1 cells and tumors. Results : The expression of amphiregulin protein was inhibited dramatically in the NS2T 2A1 cells after infection with AdA4. The in vitro cell growth was inhibited significantly at day 4 post-AdA4 infection compared with control empty virus AdC1 at a MOI of 200 and 400 pfu/cell to 69.3% and 49.8%, respectively (P<0.02, P <0.005).After 3 intra- tumoral injections of 10⁹ pfu AdA4, tumor volume was reduced to 40.6% of that in the control group at day 35 (P <0.005). Conclusion : The transfer of amphiregulin RNA antisense by an adenoviral vector is effective for amphiregulin targeting strategy, leading to an inhibition of in vitro cell proliferation and in vivo tumor growth in this breast cancer model.