Does tamoxifen stop breast cancer from growing?

Yes: Tamoxifen is an antiestrogen that blocks the ability of breast cancer cells to use estrogen; therefore, it is only effective in hormone sensitive (estrogen receptor +) breast cancers. When taken for 5 years, tamoxifen has been shown to both stop the growth of cancer cells in breast cancer patients and to prevent the development of breast cancer in women that are at high risk.

Is Possible: Tamoxifen is used as a hormone therapy in the breast cancers that exhibit an estrogen hormone receptor. (er+ tumors).