A pooled multisite analysis of the effects of female reproductive hormones on glioma risk.

Purpose: The association between female reproductive factors and glioma risk is unclear, but most published studies have been limited by small sample size. We conducted a pooled multisite study of pre- and postmenopausal women, investigating the effect of female reproductive factors, including hormonal medications.

Methods: Unconditional logistic regression was used to calculate odds ratios (ORs) and 95 % confidence intervals (95 % CIs) assessing the effects of female reproductive factors and female hormonal medications in glioma cases and unrelated controls.

Results: Menarche over the age of 15 as compared to under 12 was associated with a statistically significant risk for glioma (OR 2.00, 95 % CI 1.47-2.71). Use of oral contraceptive pills (OCP) was inversely associated with risk of glioma (OR 0.61, 95 % CI 0.50-0.74), and there was an inverse trend with longer duration of OCP use (p for trend <0.0001). Use of hormone replacement therapy (HRT) was also inversely associated with risk of glioma (OR 0.55, 95 % CI 0.44-0.68), and there was an inverse trend with longer duration of use (p for trend <0.0001). Compared to those reporting neither OCP use nor HRT use, those who reported using both were less likely to have a diagnosis of glioma (OR 0.34, 95 % CI 0.24-0.48).

Conclusions: Female reproductive hormones may decrease the risk for glioma. The association appears to be strongest with greater length of use and use of both HRT and OCP.