Studies linking migraine to breast cancer have reported inconsistent results. Furthermore, a biological mechanism underlying such an association has not been investigated although some have proposed that endogenous hormone levels, including estrogen, may be responsible because higher hormone levels have been associated with breast cancer and fluctuating levels have been shown to trigger migraines. To investigate this further, Rulla M. Tamimi, Sc.D., from the Channing Division of Network Medicine at the Department of Medicine at Brigham and Women's Hospital at Harvard Medical School in Boston, MA, and colleagues, analyzed data from 115,378 women, 17,696 of whom who reported a physician's diagnosis of migraine and found migraine was not associated with breast cancer. Furthermore, among 2034 pre-menopausal women, endogenous sex hormone levels did not differ by migraine status. The authors next performed a meta-analysis of 5 studies (including their study) and found migraine was associated with a lower risk of breast cancer overall, but when they stratified by study design this relationship was limited to the pooled case-control studies but not the pooled prospective cohort studies. The difference in findings according to study designs, may reflect additional limitations that may occur in case-control studies that can be more easily avoided in prospective cohort studies.
The authors conclude, "In this large cohort study, migraine was not associated with breast cancer risk or differences in endogenous sex hormone levels."