The researchers from the University of Oxford pooled together data on hormone levels in the blood of around 760 premenopausal women with breast cancer, and around 1700 without – from seven earlier studies.
They found that a doubling in concentration of the female sex hormones – oestradiol and oestrone – or the male sex hormones – androstenedione, dehydroepiandrosterone sulphate (DHEAS) and testosterone, increased the risk of breast cancer by between around one-fifth and around one-third.
Professor Tim Key, lead author and Cancer Research UK epidemiologist at the University of Oxford, said: “This analysis combined the results from seven previous studies to provide enough data for us to focus on the association between hormone levels and the risk of breast cancer in women before the age of 50. The results demonstrate a link between higher overall levels of 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.
“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.
“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.”
The researchers also looked at the association between sex hormone levels and other lifestyle factors, such as drinking alcohol, in premenopausal women. They found associations between some sex hormones and certain breast cancer risk factors, such as alcohol intake.
Around 10,000 women under 50 are diagnosed with breast cancer every year in the UK. The majority of cases – 40,000 – are in women over 50.
Hazel Nunn, head of health information at Cancer Research UK, said: “This is a fascinating piece of research which is helping us to understand more about the role of sex hormones and the effect they might have on breast cancer. With 1 in 5 breast cancers now diagnosed in women under 50 it’s important that we find out as much as we can about what increases the risk for younger women. We don’t yet know why having higher levels of some sex hormones might increase a woman’s risk so further research is needed to investigate this link.”
For media enquiries please contact the press office on 020 3469 8300 or, out-of-hours, the duty press officer on 07050 264 059.
1 Key, T et al (2013) Sex hormones and risk of breast cancer in premenopausal women: a collaborative reanalysis of individual participant data from seven prospective studies. The Lancet Oncology.