Pharmaceutical compositions of 4-hydroxy tamoxifen, particularly compositions suitable for percutaneous administration, are useful in methods for treating and preventing breast cancer. When percutaneously administered to a patient's 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.