Almost 20% of patients receiving ovarian function suppression (OFS) and endocrine therapy (ET) for breast cancer treatment had inadequate OFS within the first year of treatment. Few studies have explored the long-term effectiveness of OFS to maintain estrogen suppression.

This retrospective, single institution study examined premenopausal women with early-stage breast cancer undergoing treatment with OFS and ET. The primary endpoint was the percentage of patients with inadequate ovarian suppression (estradiol ≥10 pg/mL) during OFS cycle 2 or later. The secondary endpoint was the percentage of patients with inadequate ovarian suppression within the first cycle after OFS initiation. Differences in age, body mass index (BMI), and previous chemotherapy use were summarized via multivariable logistic regression.

Of the 131 patients included in the analysis, 35 (26.7%) lacked adequate suppression during OFS cycle 2 or later cycles. Patients with adequate suppression throughout treatment were more likely to be older (odds ratio [OR] 1.12 [95% CI, 1.05-1.22], P = .02), have a lower BMI (OR 0.88 [95% CI, 0.82-0.94], P < .001), and have received chemotherapy (OR 6.30 [95% CI, 2.06-20.8], P = .002). A total of 20 of 83 patients (24.1%) had an inadequately suppressed estradiol level within 35 days of OFS initiation.

This "real world" cohort demonstrates that estradiol concentrations above the postmenopausal range of the assay are frequently detected, including more than 1 year after the start of OFS. Additional research is needed to establish estradiol monitoring guidelines and optimal degree of ovarian suppression.