Study in north Chile found chemical is linked to 50 per cent drop in deaths
Scientists at University of California, Berkeley hailed findings 'astonishing'
Focused on the town of Antofagasta where arsenic levels in drinking water were found to be 80 times higher than levels recommended by WHO
Among women aged under 60 mortality was reduced by 70 per cent
Study could pave the way for new treatment to combat the disease
It is notoriously poisonous but arsenic may help cut the number of deaths from breast cancer, research suggests.
A new study carried out in Chile has linked the chemical element with a 50 per cent drop in breast cancer deaths.
The study focused on a region in the South American country where residents had been inadvertently exposed to high levels of arsenic - a naturally occurring element found in many minerals.
Instead of noting a rise in death rates, researchers found breast cancer deaths were cut in half during the period coinciding with high arsenic exposure.
The effect was more pronounced among women under the age of 60, with mortality reduced in this group by 70 per cent.
Lead author, professor Allan Smith, said: 'What we found was astonishing.
'We've been studying the long-term effects of arsenic in this population for many years, focusing on increased disease and mortality attributed to the historical exposure to arsenic in this population.'
In 1958, the northern Chilean city of Antofagasta switched to a geothermal water source originating in the Andes mountains.
Years later, it was discovered that the water sources contained more than 800 micrograms per litre of arsenic - 80 times higher than the levels recommended by the World Health Organisation.
An arsenic removal plant was installed in 1970 after some residents began to show the toxic effects from exposure.
As part of the study, researchers at the Stanford Cancer Institute found human breast cancer cells grown in the lab are killed by arsenic.
And normal breast cells were also found to be more resistant to the chemical.
The medicinal use of arsenic is not entirely new.
A new study carried out in Chile has linked the chemical element with a 50 per cent drop in breast cancer deaths. The disease is pictured under the microscope
In 1958, the northern Chilean city of Antofagasta switched to a geothermal water source originating in the Andes mountains. Years later, it was discovered that the water sources contained more than 800 micrograms per litre of arsenic - 80 times higher than the levels recommended by the World Health Organisation
Arsenic trioxide was approved in 2000 by the Food and Drug Administration in the U.S., as an effective treatment for a rare type of leukaemia.
So should the chemical be used to treat breast cancer?
Professor Smith said: 'Not yet. We do not know if the treatment will work, but carefully designed clinical trials should take place as soon as possible based on this new evidence.'
The team of scientists are in the process of designing clinical trials, in which some advanced breast cancer patients would be given arsenic treatment.
The study was published in the open-access journal EBioMedicine.