[an-tee-ES-tro-jen or an-tie-ES-tro-jen]
a substance (for example, the drug fulvestrant) that blocks the effects of estrogen on tumors. Drugs such as tamoxifen interfere with estrogen’s effects by competing for it so that it can’t get to the cancer cells. These types of drugs are used to treat breast cancers that depend on estrogen for growth. See also estrogen, hormone therapy, selective estrogen receptor modulator.