Years of hot flashes may increase the risk of breast cancer

Women who experience hot flashes and night sweats over a period of many years may have a higher risk of breast cancer, according to new research.

New US research has found that women who experience persistent hot flashes are more likely to go on to develop breast cancer than women who have never experienced the common menopausal symptoms.

Carried out by researchers at the City of Hope National Medical Center in California, the new large-scale study looked at data gathered from 25,499 postmenopausal women aged 50 to 79 who participated in the Women's Health Initiative (WHI), which consisted of three clinical trials and an observational study to investigate the major health issues causing disease and mortality in postmenopausal women.

The researchers followed the women for nearly 18 years to look at the possible association between vasomotor symptoms (VMS) -- which include symptoms such as hot flashes and night sweats -- and breast cancer.

The symptoms are common for women during menopause, but can persist for years after.

The findings, published online in Menopause, the journal of The North American Menopause Society (NAMS), showed that women with persistent VMS, defined as symptoms that lasted 10 or more years, were more likely to go on to be diagnosed with breast cancer than women who never experienced VMS.

Although death from breast cancer was also higher in women with persistent VMS, the difference was not statistically significant, meaning women with persistent VMS were not more likely to die from breast cancer than women without VMS.

Previous studies have also looked at the association between vasomotor symptoms (VMS) and breast cancer, but the results have been inconsistent. 

Hormones may also play a role in the relationship between breast cancer risk and VMS, with hormone therapy currently the most effective treatment for VMS and sex hormone levels also related to postmenopausal breast cancer risk.

"In this large group of women who were not users of hormone therapy, persistent hot flashes and night sweats for 10 or more years were associated with a slight but significant increase in breast cancer incidence," says Dr. JoAnn Pinkerton, NAMS executive director. "Other risk factors included an elevated body mass index of more than 30 and current alcohol use. More studies are needed in women who have persistent hot flashes to understand their cardiovascular and cancer risks."