Effects of vaginal estrogens on serum estradiol levels in postmenopausal breast cancer survivors and women at risk of breast cancer taking an aromatase inhibitor or a selective estrogen receptor modulator.

Background: Intravaginal estradiols (VE) have been proposed as safe alternatives to systemic estrogen therapy in breast cancer survivors.

Patients And Methods: Postmenopausal women with estrogen receptor-positive breast cancer or at high risk for breast cancer (n = 24) who were taking an aromatase inhibitor (AI) or a selective estrogen receptor modulator (SERM) and VE for ≥ 90 days for atrophic vaginitis and 24 controls taking AI only participated in the study. Serum samples were drawn from VE ring patients before insertion and 30 and 60 days postinsertion, from VE tablet patients the morning before insertion and approximately 12 hours postinsertion, and once from controls. Samples were assayed for E2 concentrations by using highly sensitive radioimmunoassay after ether extraction.

Results: Mean E2 levels in controls were 3.72 pmol/L (range, < 3.0-7.7 pmol/L); mean E2 levels preinsertion and 12 weeks postinsertion in the VE ring patients were significantly greater than controls (P < .001 for each comparison). Mean preinsertion E2 levels in patients using VE tablets were not significantly different than those of controls (P = .48), and postinsertion levels were 76 pmol/L higher than preinsertion (P < .001).

Conclusion: VE treatment increased E2 levels. Preinsertion levels for patients receiving VE tablets were not elevated compared with those of controls, suggesting that E2 elevations with this preparation may not be continuously sustained. We conclude that VE treatment, regardless of type, results in elevated circulating E2 levels in this population and should be used with caution.