The present invention provides methods for treating and preventing breast cancer by administering 4-hydroxy tamoxifen to a patient. It also provides pharmaceutical compositions of 4-hydroxy tamoxifen suitable for percutanous administration. When percutaneously administered to a patients breasts, 4-hydroxy tamoxifen concentrates locally, and exerts an anti-estrogenic effect. In patients with breast cancer, this effect reduces tumor tissue proliferation. In patients at risk for developing breast cancer, the anti-estrogenic effect prevents breast tumor formation.
