I was post menopausal age 66 when prescibed Letrozole for Er pos cancer. I took for 11 months. In that time my existing firoid did not shrink as expected. I actually grew another fibroid, developed endometriosis and an ovarian cyst. All fuelled by oestrogen! The conclusion was that the Letrozole was stimulating my pituitary gland to produce FSH. I have never had my estradiol level measured. Perhaps I should!