Breast cancer drug hist fresh safety snag

By PHYLLIDA BROWN A proposed trial of a drug to prevent breast cancer has run into trouble for the second time in two weeks. Scientists in the US have announced that the drug, tamoxifen, alters DNA in the liver cells of rats and hamsters. The researchers argue that the results may make tamoxifen ‘a poor choice’ for the prevention of cancer in healthy women. The latest findings come just as Britain’s Medical Research Council is deciding whether to fund the five-year trial, which would involve 15 000 healthy women. The MRC surprised the doctors organising the trial with an eleventh-hour announcement last month which stalled the trial. The MRC said it wanted to consider data on the drug’s toxic effects in rats from ICI, the company that manufactures tamoxifen (This Week, 29 February). The MRC has now taken the American results into account as well. The scientists in the US have published their findings in the 1 March issue of Cancer Research. Xueliang Han and Joachim Liehr at the University of Texas Medical Branch in Galveston exposed rats and hamsters to various doses of tamoxifen. They found that liver cells in the animals developed structures known as DNA adducts that bind to DNA: the more tamoxifen, the more adducts formed. Scientists believe adducts may be involved in the development of tumours, although there is no evidence of a causal link. ‘I feel that the rat data call for more studies of this material,’ says Liehr. He is cautious about interpreting the results but feels more animal tests are necessary. Meanwhile, the paper concludes: ‘The accumulation of DNA adducts with repeated administrations of tamoxifen to rodents may make this drug a poor choice for the chronic preventative treatment of breast cancer.’ The US, like Britain, plans to test the drug in healthy women. ‘This is still a preliminary study but I tried to publish it fairly rapidly because of the impending trials,’ says Liehr. This week a spokesman for ICI said that the company was aware of the new work from Texas, but did not consider that it changed the overall picture. ‘The findings are scientifically interesting, but we do not think they lead to any new conclusions.’ Meanwhile, ICI is developing a new drug which, like tamoxifen, blocks the effects of the hormone oestrogen and could be effective against breast cancer. The company confirmed this week that a new anti-oestrogen was ‘in early clinical development’ but would not give further details. Tamoxifen’s action is complex:
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