Estrogen is a hormone. It is a small molecule, so it is different from insulin or growth hormones which are peptides and proteins.
Estrogen gives cells permission to grow when appropriate. This is essential during puberty, but also necessary in adult life. For instance, estrogen is important in bone growth, and low levels of estrogens can lead to osteoporosis. But in the case of cancer, estrogen can enhance unnatural growth and make the disease worse.
SERMs (selective estrogen receptor modulator)
Tamoxifen is a SERM and is one of the most common and oldest forms of hormone therapy. SERMs like tamoxifen attach to receptors on the cancer cells which blocks estrogen from attaching to the receptors.
SERDs (selective estrogen receptor degrader)
Fulvestrant is a SERD drug that acts by damaging and blocking estrogen receptors. See also [[Target degradation]].
Aromatase is a heme-containing enzyme which oxidizes an angular methyl group to hydroxymethyl, which is then lost as formic acid in oxidative aromatization reaction. KEGG database
Anastrazol binding to aromatase.