Patients who suffer from migraine headaches are 30% less likely to develop breast cancer.  It is well established that fluctuating estrogen levels throughout the menstrual cycle can trigger migraine attacks.  These fluctuations are reduced during pregnancy and menopause, resulting in cessation of migraine attacks in two thirds of women.  At this point it is not clear what common estrogen-based mechanisms are responsible for the reduction of breast cancer risk in migraine sufferers.