Early findings from a randomised trial investigating the effectiveness of tamoxifen to prevent breast cancer are reported in this week's issue of THE LANCET. Although tamoxifen reduced breast cancer incidence by a third compared with women given placebo, the authors of the study caution that it is still too early to fully assess the risk to benefit ratio of tamoxifen as a preventative strategy for breast cancer.

Tamoxifen is well known in its effect to decrease recurrence of (and death from) breast cancer; however, three clinical trials on the use of tamoxifen to prevent breast cancer have reported mixed results. The overall evidence supports a reduction in the risk of breast cancer, but whether this benefit outweighs the risks and side-effects associated with tamoxifen is unclear.

Jack Cuzick from Cancer Research UK, lead investigator of the International Breast Cancer Intervention Study (IBIS-I) and colleagues undertook a double-blind placebo-controlled randomised trial of tamoxifen, 20 mg/day for 5 years, in around 7000 women from the UK, Europe, Australia and New Zealand who were aged 3570 years and who were at an increased risk of breast cancer (eg. They had a Family history of the disease or had a benign lesion associated with an increased risk of breast cancer).

The frequency of breast cancer was reduced by a third among Women given tamoxifen (69 breast cancers in 3578 women in the tamoxifen group and 101 breast cancers in 3566 in the placebo group). Endometrial cancer--considered to be increased by tamoxifen use--was doubled in the tamoxifen group (11 instances compared with 5 in the control group), but this increase was not statistically significant, and all cases were localised (stage 1) and curable by hysterectomy.

However, tamoxifen use was associated with more than a doubling in the risk of blood-clotting complications, especially after surgery or long periods of immobilisation. The investigators comment that the incre
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Contact: Richard Lane
richard.lane@lancet.com
44-207-424-4949
Lancet
12-Sep-2002

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