There is good evidence that, at least in some cancer types, not all cancer cells are equally able to divide and form tumors. The select cells that acts as the driving force in the development of cancer are known as cancer stem cells (CSC). Evidence suggests CSC are responsible for the development of breast cancer. In a recent study, researchers showed that estrogenA steroid sex hormone. Estrogen's structure is closely related to cholesterol. Produced by the ovaries, estrogen has effects on the reproductive, cardiovascular and skeletal systems. Estrogen is also a growth factor for some types of cells, including breast cells. Inhibitors of estrogen function such as tamoxifen and arimidex are used to block the growth effects of estrogen. See also, estrogen receptor. reduces the number of CSC in normal and cancerous breast tissue. The results may partially explain why cancers that are estrogen receptorA protein located within cells that binds estrogen. The protein:estrogen complex then binds to DNA to increase the transcription of certain genes, and therefore is a type of transcription factor. The estrogen receptor is the target of the anticancer drug tamoxifen. By binding to the estrogen receptor tamoxifen blocks the growth promoting effects of the hormone. May be abbreviated as ER. positive tend to have better prognoses.
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