Definition of Menopause There are various definitions of menopause used in breast cancer clinical trials. Menopause is usually the permanent cessation of menstruation and, as a term used in breast cancer treatment, includes an extreme and persistent decrease in ovarian estrogen synthesis. Reasonable criteria for determining menopause include any of the following: 1) previous bilateral oophorectomy; 2) age ≥60 years; 3) age <60 years and amenorrhea for 12 months or more without chemotherapy, tamoxifen, toremifene or ovarian suppression and follicle stimulating hormone (FSH) and estradiol are within the postmenopausal range; 4) if taking tamoxifen or toremifene and age <60 years 4. if taking tamoxifen or toremifene and aged <60 years, plasma follicle stimulating hormone (FSH) and estradiol levels are within the post-menopausal range. Determining menopausal status is not possible for women receiving luteinizing hormone-releasing hormone agonists or antagonists. In premenopausal women at the start of adjuvant chemotherapy, amenorrhea is not a reliable indicator of menopausal status because ovarian function may still be intact or recover after chemotherapy despite anovulation/amenorrhea. In women with amenorrhea caused by these treatments, if aromatase inhibitors are considered as part of endocrine therapy, ovariectomy or serial measurement of follicle stimulating hormone and/or estradiol is required to ensure postmenopausal status.