Increased levels of sex hormones in urine, often a result of obesity, warn of a heightened risk of breast cancer, according to a new study in the British Journal of Cancer1.

The investigation, a collaboration between Dutch researchers and a leading Cancer Research UK scientist in Oxford, is the largest study to date on sex hormones in urine and their effect on breast cancer risk. It found that postmenopausal women with high amounts of certain types of oestrogen and testosterone in their urine were at a greater risk of developing the disease.

Obesity is the biggest known reason for high levels of sex hormones among postmenopausal women. Cancer Research UK scientists believe that maintaining a healthy weight could help women bring down their breast cancer risk.

Earlier studies by Cancer Research UK have already established the link between increased levels of sex hormones in the blood and breast cancer.

In this study researchers measured the levels of two forms of oestrogen and two forms of testosterone in urine samples from hundreds of postmenopausal women. For each of the hormones tested, scientists compared the women with the highest urine levels and those with normal levels.

They found that the group of women with the highest levels of one form of oestrogen – called oestrone – also had more than double the rate of breast cancer cases.

The group of women with the highest level of a type of testosterone had rates that were 70 per cent higher than the women with normal levels.

Dr Petra Peeters of the Utrecht University Medical Centre in Holland, says: “We know that reproductive and hormonal factors are involved in the development of breast cancer. This study confirms that high levels of sex hormones can raise risk.”

Fellow researcher Dr Tim Key of the Cancer Research UK Epidemiology unit at Oxford University, says: “This provides further evidence of the link between hormones and the risk of breast cancer.”

Dr Key explains that fat cells produce excess amounts of the hormone oestrogen, which can speed up the natural process of cell division. The faster cells duplicate, the higher the chance that something can go wrong and that a cancer cell may form.

“In the future it might become possible to use the presence of sex hormones in urine to help monitor a woman’s risk and to target screening at women who need it most,” he adds.

Sir Paul Nurse of Cancer Research UK, which owns the British Journal of Cancer, says: “This study furthers our understanding of the disease and provides another avenue to explore in the prevention and diagnosis of breast cancer.”


  1. British Journal of Cancer88 (9)


The study was part of a project investigating the effectiveness of early breast cancer screening. 27,718 women living around the Utrecht area of the Netherlands took part in the project from 1975 until 1996. This study collected urine samples from 9,349 eligible postmenopausal women with no history of breast cancer. The researchers examined the samples from the 364 women that developed breast cancer within the eligible group and a further 382 random samples taken from the eligible group.

Researchers monitored two forms of oestrogen (oestrone, oestradiol); testosterone and another hormone related to testosterone – 5a-androstane-3a, 17b-diol.

In the group of women with the highest level of oestrone the rate of cases was 2.5 as many as the normal population. In the group of women with the highest level of oestradiol it was 1.5 as many cases; with the highest level of testosterone it was 1.6 as many cases; and with the highest level of 5a-androstane-3a, 17b-diol it was 1.7 as many cases. Only the rates for oestrone and 5a-androstane-3a, 17b-diol were statistically significant.

The study was carried out by Utrecht University Medical Centre and supported by the Dutch Cancer Society, Cancer Research UK and the International Agency for Research on Cancer (IARC).

Women on HRT or taking oral contraceptives were excluded from the study.