Breast cancer drug raises risk of killer secondary tumour

Published on Tuesday 25 August 2009 20:15

LONG-TERM use of one of the most common treatments for breast cancer dramatically increases the risk of developing a deadly secondary tumour, a study has shown.

Tamoxifen is the "gold standard" hormonal therapy, given to thousands of British women to improve their chances of surviving breast cancer.

The drug blocks the ability of the sex hormone oestrogen to boost the disease.

In women with hormone-sensitive cancers, the majority of breast cancer patients, it can stop tumours returning after surgery.

But the US research shows that tamoxifen also raises the risk of developing more aggressive tumours that are not dependent on oestrogen and are difficult to treat.

The study found five or more years of treatment with the drug quadrupled the chances of an aggressive non-hormone sensitive tumour appearing opposite the initial site of the disease.

The team from the Fred Hutchinson Cancer Research Centre in Seattle assessed the history of tamoxifen use among more than 1,000 women from the Seattle region who were diagnosed with hormone-sensitive breast cancer between the ages of 40 and 79.

The patients included 367 women with both primary hormone-sensitive cancer and a second tumour, and 728 who only had a first tumour.

Nearly all the women who had additional, or "adjuvant", therapy after surgery were given tamoxifen.

Comparing patients who received tamoxifen and those who did not showed that the drug reduced the chances of oestrogen-positive breast cancer returning by 60 per cent. However, it also appeared to increase by 440 per cent the risk of an oestrogen-negative second tumour.

The association was not seen for women who took tamoxifen for less than five years.