ER in premenopausal woman

i've read that tamoxifen is more useful for postmenopausal woman than for premenopausal woman. why is that?
can you give me also a name of an artical with the full explanation?

[CCF-RN,MSN-rf]

Dear yhaskel:  Actually, for the treatment of breast cancer, it makes no difference whether a woman is premenopausal or postmenopausal.  What matters is that the tumor is estrogen receptor positive.  Tamoxifen is effective in estrogen receptor positive tumors - regardless of menopausal status.  An article discussing this was published in The Lancet in 1998.  However, you may read a nicely written summary in Dr. Susan Love's Breast Book, published 2000, pages 391-393.  

If you are referring to the use of tamoxifen for prevention in high risk women who have not had breast cancer, then it is used in postmenopausal women only.