What is tamoxifen and why is it used in cancer research?

Estrogen blocker: Hi. Tamoxifen is an estrogen receptor antagonist. Certain cancers (most notably estrogen receptor-positive breast cancer) are stimulated to proliferate in response to estrogen, and blocking estrogen action at its receptor or blocking estrogen production by blocking the aromatase enzyme have been shown to be very therapeutic. Tamoxifen is not useful in cancer research that does nor involve estrogen

Estrogen blocker: Tamoxifen is a drug which blocks estrogen receptor. Cancers which express high levels of estrogen receptor, such as some breast cancers, may respond well (shrink) to tamoxifen. It has been in clinical use for decades.