Drug 'cuts long-term cancer risk'

Tamoxifen reduces the risk of breast cancer returning long after women stop taking the drug, research suggests.

Tamoxifen, which blocks the effect of the hormone oestrogen, is used both to treat breast cancer and to prevent it among women at high risk.

But an international study of 7,145 women found the benefits lasted beyond the five-year course of treatment. Those who took the drug were 34% less likely to get the hormone-sensitive form of the disease within eight years.

Details of the International Breast Cancer Intervention Study are published in the Journal of the National Cancer Institute.

In the study, 7,145 women at increased risk of breast cancer took a daily dose of tamoxifen or a dummy drug for five years. Eight years further on, the women who took tamoxifen had a 34% reduced risk of the hormone-sensitive form of the disease.

In this group, 87 were diagnosed with hormone-sensitive breast cancer, compared with 129 in the placebo group.

Lead researcher Professor Jack Cuzick, from the Cancer Research UK Centre for Epidemiology, Mathematics and Statistics, said: "These latest results confirm that tamoxifen continues to help prevent oestrogen receptor positive breast cancer in women at an increased risk of the disease for at least five years after treatment has stopped. Additionally we found that almost all of the excess side-effects reported on tamoxifen do not continue after treatment stops."

Tamoxifen has been linked to an increased risk of blood clots.

Professor Tony Howell, from the South Manchester University Hospitals Trust, also worked on the study. He said: "Previous studies have already shown that tamoxifen lowers the risk of developing breast cancer during active preventive treatment but this is the first time that clear evidence is available on the benefits and side-effects of tamoxifen after treatment with the drug has stopped."

Kate Law, director of clinical trials at Cancer Research UK, said it was important to offer women with breast cancer as many treatment options as possible.

In a second study conducted by the Royal Marsden Hospital in London, researchers analysed 20-year data on tamoxifen, and found it cut the risk of hormone-sensitive breast cancer by 39%. Research published this month suggests that many more lives could be saved if women with hormone-sensitive breast cancer were initially given tamoxifen, and then switched to another drug, exemestane, after two to three years.

Breast cancer is by far the most common cancer for women with more than 44,091 new cases in the UK in 2003.