Background and purpose
It is currently unknown whether vaginal oestradiol is associated with development of meningioma and glioma. The aim of this study was to examine associations between cumulative use and treatment intensity of vaginally administered oestradiol tablets and incidence of meningioma and glioma in a nationwide, population-based study.

Methods
We conducted a nested case–control study within a nationwide cohort of Danish women followed from 2000 to 2018. The cohort consisted of 590,676 women aged 50–60 years at study start, without prior cancer diagnosis or use of systemic hormone therapy. Information on cumulative dose, duration, and intensity of vaginal oestradiol tablet use was assessed from filled prescriptions. Conditional logistic regression provided adjusted hazard ratios (HRs) for the association between vaginal oestradiol use and diagnosis of meningioma or glioma.

Results
We identified 1108 women with meningioma and 835 with glioma. Of these, 19.8% and 14.0% used vaginal oestradiol tablets, respectively. The HRs in those with ever-use of vaginal oestradiol tablets was 1.14 (95% confidence interval [CI] 0.97–1.34) for meningioma and 0.90 (95% CI 0.73–1.11) for glioma. The corresponding HRs for new users exclusively were 1.18 (95% CI 0.99–1.40) for meningioma and 0.89 (95% CI 0.71–1.13) for glioma. Intensity of vaginal oestradiol tablet use according to duration and user status yielded slightly elevated HRs for meningioma without an apparent dose–response pattern, while the HRs for glioma were generally below unity. Among new users, the HR with high intensity of current or recent vaginal oestradiol tablet use for 2+ years was 1.66 (95% CI 1.09–2.55) for meningioma and 0.77 (95% CI 0.41–1.44) for glioma.

Conclusion
Use of vaginal oestradiol tablets was associated with a slightly increased incidence of meningioma but not of glioma. Owing to the observational nature of the study, residual bias cannot be ruled out.