High levels of sex hormones tied to breast cancer risk

Younger women with high levels of sex hormones in their blood are at an increased risk of breast cancer, a new Oxford study has found.

The researchers looked at data on hormone levels in the blood of up to 760 premenopausal women with breast cancer and 1,700 without, from seven earlier studies.

They found that women who had the highest levels of sex hormones were at an increased risk of breast cancer of between a fifth and a third, compared with women with the lowest hormone levels.

These were the 'female' sex hormones oestradiol and oestrone, and 'male' sex hormones androstenedione, dehydroepiandrosterone sulphate (DHEAS) and testosterone.

"While the link between higher levels of sex hormones and breast cancer is well established in older, postmenopausal women, it's much less clear what effect hormones have on cancer risk in younger, premenopausal women," said lead author Professor Tim Key of the Cancer Epidemiology Unit at the University of Oxford.

"But from this study we can say there appears to be a link, which has important implications for understanding the biology of breast cancer and for planning future research.

"This analysis combined the results from seven previous studies to provide enough data for us to focus on the association of hormone levels with the risk for women developing breast cancer before the age of 50.

"The results demonstrate a link between higher overall levels of the female sex hormones and breast cancer in premenopausal women - although due to the large variation in hormone levels over the menstrual cycle these findings cannot be used now to classify the risk for individual women," Key said.

The researchers also looked at the association between increased hormone levels in premenopausal women and other lifestyle factors, such as drinking and smoking.

They found that women who smoked 15 or more cigarettes a day, or drank two or more glasses of wine a day, had higher levels of the male sex hormones compared with women who didn't smoke or didn't drink. Women who drank the most alcohol also had higher levels of oestrogens.