Researchers from the Fred Hutchinson Cancer Center in Seattle interviewed more than 1,000 women with one of three kinds of breast cancer and compared them to nearly 500 randomly selected women of similar ages with no history of breast cancer.
Participants were asked whether they ever experienced menopausal symptoms, including hot flashes, sweating or night sweats, vaginal dryness, bladder problems, irregular or heavy menstrual bleeding, depression, anxiety, insomnia, or emotional distress.
With regard to hot flashes, women were asked how often they occurred, how long they typically lasted, and for how many total weeks or months they had them.
Compared to women who reported never having menopausal symptoms, those who had experienced symptoms had half the risk of invasive ductal carcinoma or invasive lobular carcinoma, two of the most common types of breast cancer.
And the more frequent or severe the hot flashes were, the lower their risk appeared to be.
Those associations remained even after researchers took into account other things that are known to influence breast cancer risk, such as the use of hormone replacement therapy, age at menopause, and body weight.
The study is published in the February issue of Cancer Epidemiology, Biomarkers & Prevention.
Hot Flashes and Breast Cancer
“This is the first study to ever look at this association,” says study researcher Christopher I. Li, MD, PhD, a breast cancer epidemiologist in the Hutchinson Center’s Public Health Sciences Division.
Li stresses, however, that his study was not designed to show cause and effect, and that the connection between menopausal symptoms and breast cancer is still largely a mystery.
“We don’t know a whole lot about all the biology that’s at work here,” he says.
In particular, scientists don’t know what causes hot flashes, only that they appear to be linked to lower levels of the hormone estrogen.
Breast cancer, in turn, has been linked to higher levels of estrogen, so it may be that hot flashes are acting as a marker for the intensity of hormonal changes in the body, Li says.
Indeed, a previous study showed that women who experienced hot flashes several times a day had 35% to 45% lower estrogen levels compared with women who did not experience hot flashes or who only experienced them infrequently.