Vaginal estriol to overcome side-effects of aromatase inhibitors in breast cancer patients.

Objective: Aromatase inhibitors are essential as endocrine treatment for hormone receptor-positive postmenopausal breast cancer patients. Menopausal symptoms are often aggravated during endocrine treatment. We investigated whether vaginal estriol is a safe therapeutic option to overcome the urogenital side-effects of aromatase inhibitors. Serum hormone levels were used as the surrogate parameter for safety.
Methods: Fasting serum hormone levels of ten postmenopausal breast cancer patients receiving aromatase inhibitors were prospectively measured by electro-chemiluminescence immunoassays and gas chromatography/mass spectrometry before and 2 weeks after daily application of 0.5 mg vaginal estriol (Ovestin® ovula), respectively.
Results: Two weeks of daily vaginal estriol treatment did not change serum estradiol or estriol levels. However, significant decreases in levels of serum follicle stimulating hormone (p = 0.01) and luteinizing hormone (p = 0.02) were observed. Five out of six breast cancer patients noticed an improvement in vaginal dryness and/or dyspareunia.
Conclusions: The significant decline in gonadotropin levels, indicating systemic effects, has to be kept in mind when offering vaginal estriol to breast cancer patients receiving an aromatase inhibitor.