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A common drug to treat breast cancer increases the risk of an aggressive secondary tumour developing if used for a long time, research reported in the journal Cancer Research has shown.
Tamoxifen is prescribed to thousands of women in the UK to help them fight breast cancer. It prevents oestrogen from fuelling tumours by blocking the sex hormone’s ability to do so.
But using the drug also increases the risk of developing new tumours not dependent on oestrogen that are more aggressive and difficult to treat, the research suggests.
A team led by Dr Christopher Li, from the Fred Hutchinson Cancer Research Centre in Seattle, found that tamoxifen quadrupled the risk of developing a deadly tumour not dependent on oestrogen opposite the initial site of the cancer.
More than 1,000 women from the Seattle region between 40 and 79 years diagnosed with hormone-sensitive breast cancer were assessed for use of the drug. Nearly all of those who had to undergo additional therapy after surgery were prescribed tamoxifen.
The researchers found that the risk of oestrogen-positive breast cancer was reduced by 60% after using the drug. But it also seemed to increase the chance of developing a second oestrogen-negative tumour by 440%.
There was no link for who took tamoxifen for less than five years.
“It is clear that oestrogen-blocking drugs like tamoxifen have important clinical benefits and have led to major improvements in breast cancer survival rates,” said Dr Li. “However, these therapies have risks, and an increased risk of ER negative second cancer may be one of them.
Copyright Press Association 2009