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Wednesday, 20 March, 2002, 13:41 GMT
Tamoxifen prevents breast cancer
Tamoxifen - 'imdisputable benefits'
Tamoxifen - 'imdisputable benefits'
Taking tamoxifen can reduce the incidence of breast cancer in healthy women who are at high risk of the disease by a third, researchers have found.

Early results from the International Breast Cancer Intervention Study (IBIS) were presented to the European Breast Cancer Conference in Barcelona on Wednesday.

Doctors say the benefits of treating high-risk women with tamoxifen are "indisputable". Results from the previous studies had been mixed.

But they admit they do not yet know if those benefits outweigh the risk of side effects, such as developing blood clots.

Tamoxifen can prevent breast cancer in healthy women at high risk of the disease  

Professor Gordon McVie, Cancer Research UK
Tamoxifen is given to women who have already had a tumour in their breast removed to prevent the cancer returning.

The IBIS study involves more than 7,000 healthy women from around the world who are at increased risk of breast cancer.

Half are taking tamoxifen, and half a dummy tablet.

There were a third fewer cases of breast cancer in women taking tamoxifen compared to those who were not - 68 and 101 respectively.

When scientists looked at results from all the studies into tamoxifen as a preventative treatment, the overall reduction was 38%.

The benefit was the same for women whatever their age, level of risk and whether or not they were taking hormone replacement therapy.

However, tamoxifen was only effective at reducing incidence of a certain type of cancer called oestrogen receptor positive (hormone positive) cancers.

It had no effect on cancers that were oestrogen receptor negative.


The IBIS study also found there was a two to three-fold increase in the risk of endometrial cancer and a two to three-fold increase in the risk of blood clots for women taking tamoxifen.

The risk of blood clots was linked to surgery or immobility.

The researchers say, as a precaution, women should stop taking tamoxifen before major surgery, or be given anti-clotting treatments during the procedure.

Similar precautions should apply to women who become immobile.

Where tamoxifen was given as an additional treatment of breast cancer showed a 46% reduction in the incidence of second cancers in the opposite breast.

Women undergo breast screening to check for tumours
Women undergo breast screening to check for tumours
The IBIS study has seen 25 deaths in total in women taking tamoxifen, compared to 10 in the group who are not.

Deaths from cancers other than breast were higher in the tamoxifen group, but the numbers of these cancers were not increased, so experts say this was likely to be a chance finding.

IBIS lead investigator Professor Jack Cuzick, who is from Cancer Research UK, said: "These results are preliminary and it is essential to continue to follow the participants to see if a particular high risk group of healthy high-risk women can be identified for whom the benefits of tamoxifen clearly outweigh any risks."

He added: "For high risk women, we calculate that deaths from breast cancer within 10 years of diagnosis would be reduced by 18%."

He said efforts should be taken to reduce the blood clot risk associated with tamoxifen as a preventative drug, but added the risk was about the same as that faced by a woman taking HRT.


Professor Cuzick added: "If you are a breast cancer patient taking tamoxifen for treatment it is absolutely essential that you continue the treatment.

Professor Gordon McVie, joint director general of Cancer Research UK, said: "These preliminary findings confirm that tamoxifen can prevent breast cancer in healthy women at high risk of the disease.  

"The results so far show that incidence was reduced by one-third, compared to women taking a placebo. These findings are obviously very encouraging."

Delyth Morgan, chief executive of Breakthrough Breast Cancer, said the IBIS findings were "promising".

She added: "Breakthrough welcomes anything that can reduce a woman's chances of getting breast cancer. However more research is needed and this trail is still at an early stage.

"Women currently receiving tamoxifen for the treatment of breast cancer should not be put off using this drug. There is a great deal of evidence to suggest that tamoxifen can be beneficial for some women who have had breast cancer and that these benefits outweigh the risks."

See also:

19 May 00 | Medical notes
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