Women who get migraines have a significantly lower risk of breast cancer, according to a new report.

"We found that, overall, women who had a history of migraines had a 30 percent lower risk of breast cancer compared to women who did not have a history of such headaches," said Dr. Christopher Li, a breast-cancer epidemiologist at the Hutchinson Center's Public Health Sciences Division.

The results were especially true for the most common types of breast cancer, which are positive for either estrogen or progesterone receptors. Those types respond to hormones and are thus more responsive to hormone-blocking drugs.

Li said he suspects that changing levels of hormones in the body link the headaches and cancer.

"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," Li said. Patients tend to suffer fewer migraines during the off week in a cycle of birth-control pills, as well as during the third trimester of pregnancy.

Li said this is the first study to link breast cancer and migraines.

"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," he said.

For the study, the researchers combined data from 3,412 Seattle-area postmenopausal women, 1,938 of whom had been diagnosed with breast cancer and 1,474 of whom had no history of breast cancer, who served as a comparison group.

A news release on the study did not give details such as the rates of breast cancer in each of the groups.

The report appears in the November issue of Cancer Epidemiology, Biomarkers and Prevention.