Breast Cancer Risk Lower for Women with Migraine

SAN FRANCISCO, July 9 (MedPage Today) -- The reduced risk of breast cancer seen in women with migraines appears to hold regardless of menopausal status and exposure to migraine risk factors, a large study affirmed.

Risk of breast cancer was 21% lower in premenopausal women with a history of migraine and 26% lower in postmenopausal migraineurs than in those without a clinical migraine diagnosis, Christopher I. Li, MD, PhD, of the Fred Hutchinson Cancer Research Center in Seattle, and colleagues found.

The reduction in risk was not attenuated by use of prescription migraine medications or by absence of migraine triggers, such as alcohol, exogenous hormones, and smoking, they reported in Cancer Epidemiology, Biomarkers & Prevention.

The same research group last year reported the first evidence of this association.

That smaller population-based study revealed 33% lower risk of ductal carcinoma and 32% lower risk of lobular carcinoma in women with migraines.

Whereas the earlier study did not rule out bias from common factors, "this new study definitely makes the link more certain," commented Joann Elmore, MD, MPH, of the University of Washington in Seattle, who was not involved in the study.

However, she cautioned that women with migraine should not take false reassurance from the results or stop routine screening for breast cancer.

Many women diagnosed with breast cancer have no known risk factors, and reduced risk doesn't mean no risk, she noted.

From a biology standpoint, though, Dr. Elmore called the findings exciting in potentially pointing to new mechanisms that could be exploited for breast cancer prevention.

Both breast cancer and migraine have a hormonal component, making the association biologically plausible, Dr. Li's group said.

To further investigate the relationship, they analyzed the Women's Contraceptive and Reproductive Experiences Study, a population-based case-control study of 4,568 women ages 35 to 64 years diagnosed with invasive breast cancer between 1994 and 1998 in metropolitan areas across the country along with 4,678 controls.

A history of clinically diagnosed migraine reported in structured in-person interviews was associated with a 26% reduced risk of breast cancer overall (odds ratio 0.74, 95% confidence interval 0.66 to 0.82).

The breast cancer risk reduction was similar for postmenopausal women (OR 0.74 for migraine history, 95% CI 0.62 to 0.87) and premenopausal women (OR 0.79, 95% CI 0.67 to 0.93).

Nor did the relationship differ by age at migraine diagnosis (P=0.84) or by history of ever using prescription migraine medications, which served as a proxy for more severe migraine (P=0.11).

The association was seen across races (OR 0.77 with migraine history in white women and OR 0.67 in black women).

In an analysis restricted to women without exposure to migraine triggers that are also related to breast cancer risk, the results were similar for:

• Women who never drank alcohol over the past 10 years (OR 0.79, 95% CI 0.68 to 0.92)
• Women who never smoked (OR 0.76, 95% CI 0.65 to 0.90)
• Women who never used oral contraceptives (OR 0.67, 95% CI 0.52 to 0.87)
• Women who never used menopausal hormone replacement therapy (OR 0.76, 95% CI 0.66 to 0.88)

As in the earlier study, Dr. Li's group found reduced risk of both ductal (OR 0.74, 95% CI 0.66 to 0.83) and lobular (OR 0.73, 95% CI 0.57 to 0.93) carcinomas with history of migraine.

And they again found a stronger association with estrogen and progesterone receptor-positive tumors than with hormone receptor-negative tumors (P=0.04), supporting the purported biologic link.

The researchers cautioned that their study did not control for nonsteroidal anti-inflammatory drug (NSAID) use.

But "although this may explain part of the association," they noted meta-analyses have found only a 12% reduction -- less than half that observed with migraine history -- in breast cancer risk for women classified as ever using any NSAID without a greater effect for high intake.

The study was supported by the National Institute of Child Health and Human Development, contracts with the National Cancer Institute, and an intra-agency agreement with the CDC.

The researchers reported no conflicts of interest.

Dr. Elmore reported serving as an editor for the Foundation for Informed Medical Decision Making and has served as an expert witness on risk communication.

Primary source: Cancer Epidemiology, Biomarkers & Prevention Source reference: Li CI, et al "Relationship between migraine history and breast cancer risk among premenopausal and postmenopausal women" Cancer Epidemiol Biomarkers Prev 2009; 18: 2030-34.