Women who have experienced hot flushes and other symptoms of menopause may have a 50 percent lower risk of developing the most common forms of breast cancer than postmenopausal women who have never had such symptoms, according to a recent study by researchers at Fred Hutchinson Cancer Research Center.

The results of the first study to examine the relationship between menopausal symptoms and breast cancer risk are available online ahead of the February print issue of Cancer Epidemiology Biomarkers and Prevention.

The protective effect appeared to increase along with the number and severity of menopausal symptoms, according to senior author Christopher I. Li, M.D., Ph.D., a breast cancer epidemiologist in the Hutchinson Center's Public Health Sciences Division.

"In particular we found that women who experienced more intense hot flushes - the kind that woke them up at night - had a particularly low risk of breast cancer," he said.

Li and colleagues suspected a link between menopause misery and decreased breast cancer risk because hormones such as estrogen and progesterone play an important role in the development of most breast cancers, and reductions in these hormones caused by gradual cessation of ovarian function can impact the frequency and severity of menopausal symptoms.

"Since menopausal symptoms occur as hormone levels fluctuate and drop, we hypothesized that women who experienced symptoms such as hot flushes and night sweats - particularly frequent and severe symptoms - might have a lower risk of breast cancer due to decreased estrogen levels," he said.

Indeed, the researchers found a 40 percent to 60 percent reduction in the risk of invasive ductal and invasive lobular carcinoma - the two most common types of breast cancer - among women who experienced hot flushes and other symptoms. The association between such symptoms and decreased cancer risk did not change even after the researchers accounted for other factors known to boost breast cancer risk, such as obesity and use of hormone replacement therapy.

For the study, which was funded by the National Cancer Institute, Li and colleagues interviewed 1,437 postmenopausal Seattle-area women, 988 of whom had been previously diagnosed with breast cancer and 449 of whom had not, who served as a comparison group. The women were surveyed about perimenopausal and menopausal symptoms ranging from hot flushes, night sweats and insomnia to vaginal dryness, irregular or heavy menstrual bleeding, depression and anxiety.

"While menopausal symptoms can certainly have a negative impact on quality of life, our study suggests that there may be a silver lining if the reduction in breast cancer risk is confirmed in future studies," Li said. "If these findings are confirmed, they have the potential to improve our understanding of the causes of breast cancer and improve approaches to preventing this disease."