Changes in serum estradiol levels with Estring in postmenopausal women with breast cancer treated with aromatase inhibitors

Background: Anti-estrogen therapy is an effective intervention for preventing reoccurrence of hormone receptor-positive breast cancer in women. However, the side effects of anti-estrogen therapy, including urogenital symptoms, have been reported to cause significant morbidity. There is controversial data, mainly due to small sample sizes, reporting on the safety and efficacy of using vaginal estrogen to treat urogenital symptoms in patients on aromatase inhibitor therapy. Methods: We proposed a prospective trial to measure the change in blood estradiol levels in postmenopausal women with hormone receptor-positive breast cancer undergoing treatment with aromatase inhibitors when treated with vaginal estrogen preparation, Estring, for their urogenital symptoms. Only 8 prospective patients were enrolled, and the study was amended to include 6 retrospective patients who were treated similarly. Blood estradiol levels were measured at baseline and at week 16 for all patients. Results: The median age for all patients was 55 years, and the majority of them were treated with anastrozole. There was no significant difference between baseline and week 16 estradiol levels (p = 0.81). In addition, patients in the prospective group reported subjective improvement in their vaginal dryness symptoms questionnaires. Conclusions: The vaginal estrogen preparation, Estring, did not cause persistent elevations in serum estradiol levels and might be a safer option for women with significant urogenital symptoms requiring estrogen therapy. Implications for cancer survivors: Vaginal estrogen preparation, Estring, might be an option for women with hormone receptor positive breast cancer who have persistent urogenital symptoms.