A new study has reported that postmenopausal women with a history of migraine headaches have a lower risk of hormone receptor positive (ER+/PR+) breast cancer than women without such a history. Migraine headaches and breast cancer both are influenced by hormones. While two previous studies have reported similar results, this is the first study to examine whether the association is influenced by nonsteroidal anti-inflammatory drug (NSAID) use. This is an important consideration since other studies have found that NSAID use is also associated with lower risk of breast cancer.

The study included 91,116 postmenopausal women who had enrolled in the Women's Health Initiative Observational Study prospective cohort during the period 1993 to 1998. As of September 15, 2005, a total of 4,006 eligible study participants had been diagnosed with invasive breast cancer. Women with a self-reported history of migraine headaches were found to have a modestly lower risk of breast cancer than women without such a history and this risk was not found to vary by recent use of NSAIDs. When stratified by breast cancer type, the risk reduction was found to be confined to hormone receptor positive tumors; no reduction in risk was found for hormone receptor negative (ER-/PR-) breast cancer.

This study has been criticized

Despite its enormous size, this study has already been subjected to a fair amount of criticism, especially by experts in headaches. The fact that the headaches were self-reported make the data less valid than if they had been confirmed with medical records. While it is generally recognized that falling estrogen levels can be an important trigger for migraines in many women, some experts disagree with the implication that women subject to migraines have generally lower levels of estrogen than those who are not.

Hormone fluctuations and migraines in women

Migraine headaches in many premenopausal women are associated with downward fluctuations in estrogen. In such women, the likelihood of a migraine is higher immediately before or during menstruation, when estrogen levels decline, and it also is higher during the hormone-free week of birth control pill use. On the other hand, migraines are less likely during pregnancy in such women, when estrogen levels remain elevated. It is not clear why falling estrogen levels trigger migraines in some women and not others. Many women experience a substantial decrease in migraine headaches after menopause when estrogen levels are low and do not fluctuate greatly. This has led some observers to the conclusion that a steady level of estrogen, whether high or low, is preventive of migraine headaches.

Treatment for those with migraines

NSAIDs, selective serotonin receptor agonists (triptans), and hormone therapy such as estrogen patches are all used to treat so-called menstrual migraines. Two small studies have also found that combinations of phytoestrogens such as genistein and daidzein (both found in soy), black cohosh, and dong quai are effective in reducing the frequency of such migraines.

Caution is advised in using hormonal treatments for migraines

It is not necessary for women who get menstrual migraines to have lower levels of estrogen than those who do not for an association between such migraines and lower risk of breast cancer to hold. While the association appears to be based on hormonal factors, it could be the result of individual differences in sensitivity to estrogen or other genetic factors that have yet to be uncovered.

Our concern is that mitigating such migraines using hormonal treatments (including phytoestrogens) could not only eliminate any breast cancer risk advantage, but actually increase the risk of breast cancer.

Birth control pills and other forms of hormonal contraception have been found to increase the subsequent risk of breast cancer when started at a young age. Hormone replacement therapy (HRT) has been found to increase the risk of breast cancer, especially estrogen receptor positive (ER+/PR+ and ER+/PR-) and lobular breast cancer. Genistein and daidzein have been shown to inhibit breast cancer cell proliferation in some studies, but other studies have found that they can promote chromosomal damage in normal breast cells and promote the growth of late-stage breast cancer cells. Several herbal supplements designed to treat menstrual problems, and containing black cohosh, dong quai and other sources of plant-based estrogens, have been found to promote the growth of hormone receptor positive breast cancer cells. Hormonal manipulation is in any case not the first-line treatment for estrogen-withdrawal headaches. Although no studies have examined the effect of hormonal treatments for migraines on breast cancer risk, we advise caution in the absence of evidence that such treatments are safe.