EDITOR, - Rivalry among pharmaceutical companies and their products is a fact of modern life. But Gary M Williams overstates concerns about tamoxifen, and, in suggesting that toremifene, an antioestrogen that is not yet approved for treating advanced breast cancer in Britain or the United States, should be substituted for tamoxifen in prevention studies, he is suggesting the use of a drug whose long term toxicological effects in women are unknown.1 The rationale for his recommendation is that large doses of tamoxifen cause liver tumours in rats but toremifene does not.2 Had I found that tamoxifen was producing liver tumours in rats two decades ago I would not have advocated long term adjuvant tamoxifen treatment for node …