Tamoxifen vs. Letrozole

I have BC with mets to bone and brain .27 yrs old with estrogen positive tumors. I have been hearing a lot about Letrozole working better than Tamoxifen , as far as longer survival. I asked my Doc. and he said he wants to keep me on Tamoxifen.Should i insist that he change me to Letrozole ??? I'm very worried , I want to live as long as possible, I have 3 young daughters.

[CCF-RN,MSN-JS]

Dear Angel3430,  Letrozole and tamoxifen are both forms of hormone therapy, which are used to suppress estrogen in estrogen positive breast cancers.  They each work in a different way.  Tamoxifen works by directly blocking estrogen.  Letrozole blocks the enzyme aromatase, which is needed by the body to convert hormones, called androgens into estrogen.  By blocking aromatase, production of estrogen is slowed or stopped.

After menopause, conversion of androgens in muscle, skin, fat, and breast by aromatase results in relatively low, but generally stable level of circulating estrogen.  So with an aromatase inhibitor such as letrozole, a significant decrease in circulating estrogen can be accomplished.  In pre-menopausal women earlier forms of aromatase inhibitors were not able to suppress estrogen levels enough, due to high levels of other hormones, which are normal in pre-menopausal women.  Because of this aromatase inhibitors are not usually prescribed for pre-menopausal women.  It is not known at this time if newer forms of aromatase inhibitors such as letrozole will result in the same problem for pre-menopausal women, but to be on the safe side letrozole is currently recommended only for post-menopausal women.