Letrozole blocks the enzyme aromatase, which is needed by the body to convert hormones, called androgens
. 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.