The women were asked if they had ever been diagnosed with migraine by a health professional.
The researchers found that women who suffered migraines were 30 per cent less likely to develop breast cancer. In particular, migraine history appeared to reduce the risk of the most common subtypes, estrogen and progesterone-receptor.
Lead researcher Dr Christopher Li, from the Fred Hutchinson Cancer Research Centre, said: 'Migraines seem to have a hormonal component. They occur more frequently in women, and their triggers are associated with hormones.
'While these results need to be interpreted with caution, they point to a possible new factor that may be related to breast-cancer risk.'
