Tamoxifen may lead to new breast cancer

A new US study shows that women taking tamoxifen to control cancer in one breast have a greatly increased risk of developing a tumour in the other breast.

Between 1990 and 1998, researchers followed nearly 9000 women who were diagnosed with a primary localised or regional invasive breast cancer in one breast only.

The women were aged 50 years or older, and were receiving hormonal therapy (tamoxifen) but not chemotherapy. They were followed until either the study ended, a cancer developed in the other breast, or they died

The researchers found that, while tamoxifen apparently protects against oestrogen-receptor (ER)-positive tumours, tamoxifen users had a nearly fivefold increased risk of developing an ER-negative tumour in the healthy breast. ER-negative tumours are not only more difficult to treat, but are also associated with a high death rate and an 8-35 per cent lower five-year survival rate (J Natl Cancer Inst, 2001; 93: 1008-13).