A byproduct of cholesterol may fuel the growth and spread of breast cancer, scientists have warned.

According to Dr Donald McDonnell of Duke University Medical Center in the US, while many studies have shown a link between breast cancer and obesity, ‘and specifically that elevated cholesterol is associated with breast cancer risk', so far no mechanism to explain this has been identified.

"What we have now found is a molecule, not cholesterol itself, but an abundant metabolite of cholesterol - called 27HC - that mimics the hormone oestrogen and can independently drive the growth of breast cancer," he explained.

The hormone oestrogen feeds around three-quarters of all breast cancers. In a previous study, Dr McDonnell and his team found that 27HC behaved similarly to oestrogen in animals, so for this study they used mouse models that are very predictive of what occurs in humans.

The scientists wanted to see whether 27HC could promote breast cancer activity on its own and whether controlling this would have any effect.

The team found that 27HC was directly involved in the growth of breast tumours, as well as the metastasis (spread) of the cancer to other organs.

However, they also found that its activity was reduced if the animals were treated with anti-oestrogens of if supplementation of the cholesterol byproduct was stopped. In human terms, this means that the use of anti-cholesterol drugs, such as statins, may reduce the effect of 27HC.

These results were substantiated using human breast cancer tissue. The scientists also found a direct link between the aggressiveness of a tumour and an abundance of the enzyme that makes 27HC

"This is a very significant finding. Human breast tumours, because they express this enzyme to make 27HC, are making an oestrogen-like molecule that can promote the growth of the tumor. In essence, the tumors have developed a mechanism to use a different source of fuel," Dr McDonnell said.

He added that the findings suggest that if people keep their cholesterol in check, they may reduce their risk of developing breast cancer, whether this is via a healthy diet and/or the use of statins.

Details of these findings are published in the journal, Science.