CONFERENCE UPDATE (ASCO 2025)
SEER-MHOS analysis supports the use of local estrogen therapy in breast cancer patients
Anti-hormonal therapies such as tamoxifen and aromatase inhibitors are the cornerstone of treatment for hormone receptor-positive (HR+) breast cancer.1 However, these treatments can result in genitourinary syndrome of menopause (GSM), characterized by vaginal dryness, irritation, and discomfort, which may be alleviated by vaginal estrogen therapy.1 However, concerns about its safety in breast cancer patients may have resulted in the potentially undue avoidance of hormone-based treatments, depriving patients of needed symptomatic relief.1 During the 2025 ASCO Annual Meeting, Dr. Olivia Mitchel presented the findings from a retrospective cohort study exploring the association between vaginal estrogen use and survival outcomes in breast cancer patients, using data from the Surveillance, Epidemiology and End Results Medicare Health Outcomes Survey (SEER-MHOS) database.1
The retrospective cohort study included data from 18,620 female breast cancer patients aged ≥65 years diagnosed between 2007 and 2017 in the SEER-MHOS registry.1 Among them, 800 patients received vaginal estrogen therapy, while 17,820 did not.1 Outcomes assessed included overall mortality and breast cancer-specific mortality.1 Multivariate regression models were applied to adjust for age, race, cancer stage, treatment, and year of diagnosis.1 Subgroup analyses focused on HR+ breast cancer patients.1
Vaginal estrogen use was associated with significantly improved survival outcomes.1 Patients using vaginal estrogen demonstrated a significant reduction in overall mortality compared to non-users (HR=0.56; p<0.0001).1 This pattern persisted in HR+ breast cancer patients (HR=0.62; p=0.0007).1 Similarly, vaginal estrogen use was linked to a significant reduction in breast cancer-specific mortality (HR=0.53; p=0.014).1 Although a decrease in breast-cancer-specific mortality was also observed in HR+ patients, it did not reach statistical significance (HR=0.62; p=0.08).1 Longer duration of vaginal estrogen use was also found to be associated with a significant reduction in overall mortality.1 Patients using it for more than seven years showed a substantial decrease in mortality compared to those with shorter use (HR=0.01; p<0.0001).1
In conclusion, the findings add to a growing body of evidence showing that vaginal estrogen use does not increase the risk of overall and breast cancer-specific mortality, suggesting that local hormone therapy may be safer than previously assumed for managing GSM in patients receiving anti-hormonal treatment.1 This was consistent with findings from Dr. Mitchel’s latest round of analysis, which adjusted for a quality-of-life index, providing further support to this conclusion.1 These results challenge the long-standing concerns regarding vaginal estrogen therapy in breast cancer patients and support its judicious use for GSM management.1