In adjuvant therapy for hormone receptor-positive breast cancer, which statement correctly describes the typical use of Tamoxifen and Anastrozole with respect to menopausal status?

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The main idea being tested is that the choice of endocrine therapy in hormone receptor–positive breast cancer depends on whether a patient is premenopausal or postmenopausal, because the source of estrogen changes after menopause.

Tamoxifen blocks the estrogen receptor in breast tissue and is the traditional, standard option for premenopausal women, whose ovaries still produce large amounts of estrogen. In postmenopausal women, anastrozole and other aromatase inhibitors are particularly effective because most estrogen comes from peripheral conversion of androgens via aromatase; reducing this peripheral estrogen production lowers stimulation of any ER-positive cancer cells.

Aromatase inhibitors are not effective as monotherapy in premenopausal women unless ovarian function is suppressed, which is why they are used mainly in postmenopausal patients. So the typical practice is to use tamoxifen in premenopausal patients and anastrozole in postmenopausal patients.