Does tamoxifen help prevent breast cancer?

Yes.: Tamoxifen use may reduce the development of breast cancer in high-risk patients by about 50%. There are risks associated with tamoxifen, so the decision whether to take this medication is based upon an individual patient's risk:benefit analysis.

Yes - ER+ breast CA: The p-1 trial showed in high risk women tamoxifen decreased the risk of er+ tumors by 40-50% (no difference in er- tumors) over palcebo. The p-2 or star trial compared tamoxifen to raloxifene/evista and saw similar overall benefits with some slight variations. Recently, a new trial has shown 65% reduction benefit for the aromatase inhibitor Exemestane over placebo.

Recurrence: It prevents recurrence in women with estrogen receptor positive tumors.

And new primaries: Tamoxifen blocks estrogen and Progesterone receptors which when stimulated can cause remnant cancer cells to be stimulated to grow back and also can cause normal cells to be overstimulated to develop into new hormonally sensitive cancer. Statistically it reduces the chance of recurrence by 30% and reduces the chance of a second primary by 50%.

Secondary Prevention: Tamoxifen also can be used to prevent breast cancer in the other breast as well as "secondary prevention" of breast cancer in patients who are at higher than normal risk of developing breast cancer.