Drug can halve the risk of breast cancer

HEALTHY women at high risk of breast cancer would halve the risk of developing the disease if they took the drug tamoxifen, according to a "major research breakthrough", which could save thousands of lives.

Findings in the United States study have important implications for British women, 4,000 of whom are presently taking part in the same International Breast Cancer Intervention Study (IBIS) here.

Women taking a placebo drug may be advised to switch to tamoxifen, the Cancer Research Campaign said last night. The charity and the Imperial Cancer Research Fund, who fund the British study, will today announce what will happen to the British trial in the light of the American results.

"The results are so profound I'm speechless," said Sandy Kanicki, co- chair of the trial's Participant Advisory Board. "We don't know where we are going from here but we have taken a major step to help women reduce their incidence of breast cancer."

The National Cancer Institute in the US took the unusual step of releasing data about their trials into breast cancer prevention 14 months early after they found that women who took tamoxifen saw risk drop by 45 per cent.

The institute said its five year study - the biggest of three trials around the world - was the first ever to show that tamoxifen can reduce the incidence of breast cancer. They have notified the 13,000 women in the trial so that those who had been taking the placebo could consider starting tamoxifen therapy.

Tamoxifen, which was first introduced in 1969, is already the leading drug treatment for breast cancer and is taken by more than a million women around the world. It works by slipping into oestrogen receptors of breast cancer cells and locking up the cells, preventing them from growing and dividing.

In the trial, women aged 35 or more who were at risk of getting the disease because of family history, pre-cancerous breast lesions or age were randomly assigned to five years on either a placebo pill or tamoxifen.

There were 85 cancers reported in the group of women taking tamoxifen compared to 154 in the placebo group. All age groups showed similar reductions in breast cancer incidence.

However, researchers warned that tamoxifen did increase the women's chances of three rare but life-threatening health problems. There were 33 cases of cancer of the lining of the uterus in the tamoxifen group compared with 14 in the placebo group, 17 more cases of blood clots in the lung against six in the placebo group and 30 cases of deep vein thrombosis in the tamoxifen groups compared with 19.

"This is a real advance but it is no magic bullet," said NCI director Richard Klausner. "Only through continued research will we find preventions that are even more effective and with fewer side effects."

The tamoxifen trial in Britain has had a controversial history. It was launched four years ago but recruitment was suspended when the Medical Research Council linked tamoxifen to liver cancer in rats. Further studies have found no evidence of liver cancer in women who take tamoxifen.

Clare O'Neill, co-ordinator of the IBIS study in Britain, said that the data would have to be scrutinised. "Once this has taken place all women participating in the study will be informed of the American findings and they will decide for themselves whether to continue in the study."

Dr John Toy, director of clinical development at the Cancer Research Campaign, said the preliminary findings could prove a "major breakthrough". "The American data is impressive but we need to know whether it will stand up over time and what the long-term side effects of taking tamoxifen are."