An example: Tamoxifen

Tamoxifen (sold under the brand name of Novaldex) is an anti-estrogen drug used to treat breast cancer. It works by blocking the estrogen receptors in the cell nucleus, preventing the activation of genes that stimulate cellular division, and thus stops tumor growth.

Promising results in clinical trials led to its introduction in the market in 1970 as a treatment for breast cancer.

Today Tamoxifen, combined with other chemotherapeutic agents, is typically used to treat metastatic cancer, but also as an adjuvant treatment (which targets hidden micrometastases) to stop cancer recurrence after surgery.

Recent studies have also shown that Tamoxifen is very effective preventing breast cancer in  high-risk women .