New research confirms that a single blood sample taken years earlier could provide a representative measure of hormone levels known to be an indicator of breast cancer risk.
Scientists at The Institute of Cancer Research, London, found that blood samples measuring oestrogen levels taken from postmenopausal women 5-6 years ago are representative of the long-term sex hormone levels in their bodies.
Postmenopausal women who produce high levels of the sex hormones oestradiol and testosterone are known to be at increased risk of breast cancer, but how these hormones increase their risk is not well understood.
The findings show more clearly that sex hormone readings from blood samples remain consistent over extended periods of time, and could one day be used by doctors to predict a woman’s risk of developing breast cancer years in advance.
The study, published in the American Journal of Epidemiology, was supported by Breakthrough Breast Cancer, with additional funding from the NIHR Biomedical Research Centre at The Royal Marsden NHS Foundation Trust and The Institute of Cancer Research (ICR).
Measuring hormone levels may help doctors identify women at risk of developing breast cancer, but many breast cancer treatments change natural levels of sex hormones in women’s bodies, so blood samples must be taken before cancer develops to be useful.
Previous studies have estimated hormone levels from a blood test but there is limited information on how well a single blood sample taken in the past represents women’s oestrogen levels through later life.
ICR scientists took repeated blood samples from 119 postmenopausal women, several years apart, to see how well their oestrogen levels correlated between the two measurements.
The researchers found there was a correlation between hormone levels measured from blood samples taken over a 5-6 year period.
They also measured changes in women’s body mass index (BMI) over the same time - gaining weight increases sex hormones in postmenopausal women - but when they corrected for BMI, they found the correlation between readings was not significantly affected.
Study leader, Dr Michael Jones, Staff Scientist in Genetics and Epidemiology at the ICR, said: “It’s not been clear how representative a single blood sample is at representing long-term levels of sex hormones. Our study provides new data to improve our understanding of how postmenopausal women’s hormone levels change over time.
“We found there was a reasonably strong correlation between hormone measurements taken over several years, which is good because it implies that past blood samples can be used to estimate women’s risk of developing cancer.”
Michael E. Jones, Minouk J. Schoemaker, Megan Rae, Elizabeth J. Folkerd, Mitch Dowsett, Alan Ashworth, and Anthony J. Swerdlow, Reproducibility of Estradiol and Testosterone Levels in Postmenopausal Women Over 5 Years: Results From the Breakthrough Generations Study, Am. J. Epidemiol. 2014 179: 1128-1133.
doi: 10.1093/aje/kwu027