Darkness 'key to breast treatment'
Total darkness at night time is key to the success of breast cancer therapy, scientists have suggested.
Being exposed to light at night makes breast cancer resistant to the widely used hormonal therapy tamoxifen, they said.
Such exposure shuts off night time production of the hormone melatonin, according to researchers at Tulane University in New Orleans, in the US.
Their study, published in the journal Cancer Research, suggests that this hormone is "vital" to the success of the drug in treating breast cancer.
The researchers examined the role of melatonin on the effectiveness of tamoxifen in fighting human breast cancer cells implanted in rats.
They found that melatonin delayed the formation of tumours and significantly slowed its growth.
Steven Hill, co-leader of Tulane's Circadian Cancer Biology Group, said: "Our study does not identify how much light exposure is needed to suppress night time melatonin production, and potentially drive tamoxifen resistance in humans, but we think that it could be as little as the amount of light that comes in the window from a street light."