New research suggests that women who suffer regular migraines are significantly less likely to develop breast cancer.

Results of the study of 3,412 women, 1,938 of which had been diagnosed with breast cancer and 1,474 who had no history of the disease. Results showed that women who regularly suffered from migraines were 30% less likely to develop breast cancer than women who did not suffer from migraine.
 
The reasons behind the link between migraine and breast cancer are uncertain, however the authors suspect that it is down to fluctuations in levels of circulating hormones. "Migraines seem to have a hormonal component in that they occur more frequently in women than in men, and some of their known triggers are associated with hormones. For example, women who take oral contraceptives – three weeks of active pills and one week of inactive pills to trigger menstruation – tend to suffer more migraines during their hormone-free week," said study leader Dr Christopher Li in a news release issued by the Fred Hutchinson Cancer Research Center. "While these results need to be interpreted with caution, they point to a possible new factor that may be related to breast-cancer risk. This gives us a new avenue to explore the biology behind risk reduction. Hopefully this could help stimulate other ideas and extend what we know about the biology of the disease."

Mathes RW, Malone KE, Daling JR, Davis S, Lucas SM, Porter PL, Li CI. Migraine in Postmenopausal Women and the Risk of Invasive Breast Cancer. Cancer Epidemiology Biomarkers & Prevention. 2008;17:3116-3122.

News release: Migraines associated with lower risk of breast cancer. Fred Hutchinson Cancer Research Center. November 1st 2008.