Tamoxifen is a hormone therapy drug and can be used to treat hormone receptor- positive breast cancers. Tamoxifen attaches to the hormone receptors in the cancer cell, blocking estrogen from attaching to the receptors. This slows or stops the growth of the tumor by preventing the cancer cells from getting the hormones they need to grow.

For people with hormone receptor-positive early breast cancer, tamoxifen lowers the risk of breast cancer recurrence and death from breast cancer.

Tamoxifen is a pill taken every day for 5-10 years, but the benefits last long after the treatment period.

Findings from a large randomized clinical trial showed taking tamoxifen for 10 years reduced the risk of breast cancer recurrence and death more than taking tamoxifen 5 years. These findings led to increased use of tamoxifen for longer than for 5 years, especially among premenopausal women who can't take aromatase inhibitors and women with higher stage breast cancers.

Taking tamoxifen for a longer time also means a continued risk of health effects, such as endometrial cancer, and for premenopausal women, it may also impact fertility. Discuss the risks and benefits of taking tamoxifen for more than 5 years with a health care provider.