A breast cancer drug widely credited with reducing death rates in older women with the disease, can cause womb cancer, according to the World Health Organisation.
A WHO report, compiled by the world's leading cancer specialist, will fuel controversy over the drug tamoxifen, now taken by thousands of British women. It concludes: "There is sufficient evidence in humans of the carcinogenicity of tamoxifen of increasing the risk of a tumour originating from the inner lining of the uterus."
While there is little doubt over the benefits of tamoxifen in women with this disease, scientists are divided over its long-term use and its use as a preventive treatment in healthy women with a family history of breast cancer.
The Medical Research Council has twice refused to back preventive trials in this group of women. More recently, Dr Richard Bulbrook, a cancer scientist who conducted much of the earlier research into tamoxifen, criticised the United Kingdom drug trial which is now recruiting 20,000 women. Its aim is to determine the long-term versus short-term benefits or otherwise of the drug.
Dr Bulbrook said evidence is already strong to show that in the long term the risks of tamoxifen outweigh its benefits. He urged women who had been taking the drug for five or more years to seek medical advice.
The conclusion of the new report from International Agency for Research on Cancer, a division of WHO, was revealed at a conference in Lyons, France, last week. It provides the first definitive consensus statement of the drug's link with womb cancer. Earlier this year, a panel of state scientists in California declared tamoxifen "carcinogenic". However, they came under pressure to withhold their conclusions until the IARC report was published.
Tamoxifen has been available since 1973, but its use in breast cancer has been confirmed only in the last 10 years. It is now worth more than pounds 350m in sales annually to its manufacturer, Zeneca, almost one-fifth of the company's drug sales.
The company yesterday reacted angrily to the IARC report, claiming that it does not put "benefit and risk in the appropriate context in the clinical setting . . . it may cause unnecessary alarm to thousands of breast cancer patients being treated with tamoxifen".Reuse content