Which factors should be taken into account in perimenopausal women with early breast cancer who may become eligible for an aromatase inhibitor? Recommendations of an expert panel.

Menopausal status is a major consideration in adjuvant breast cancer therapy. The variable onset and duration of the menopausal transition and the poor predictive value of bleeding patterns and hormone levels mean many women fall naturally into a "perimenopausal" category. Women becoming amenorrhoeic during cytotoxic or endocrine treatment are also of uncertain status since ovarian function may resume even in older patients after several months without menses. The recent St. Gallen panel acknowledged that aromatase inhibitors (AIs) should form part of standard endocrine therapy for postmenopausal women with receptor-positive tumours. Among perimenopausal women at sufficiently high risk of recurrence, there may also be a case for adjuvant AIs either up-front or after tamoxifen. Such treatment should be initiated only after careful consideration of the patient's age, menstrual history and the effects of tamoxifen (which may make hormone levels an unreliable guide to ovarian function). In treatment-naïve women whose postmenopausal status cannot be confirmed by reliable, serial hormone measurements, treatment should start with tamoxifen. Serial monitoring of hormone levels may enable an AI to be started if postmenopausal status is confirmed. In women with treatment-induced amenorrhoea, any decision to start an AI requires baseline hormone levels consistent with postmenopausal status; and continuation of treatment requires that hormone levels remain postmenopausal during regular monitoring.