Response to a specific antioestrogen (ICI 182780) in tamoxifen-resistant breast cancer.

We treated 19 patients with advanced breast cancer resistant to tamoxifen with a new specific antioestrogen (ICI 182780) which, in animal studies, has no agonist activity. 13 (69%) patients responded (7 had partial responses and 6 showed no change) to monthly intramuscular injections of ICI 182780 after progression on tamoxifen, for a median duration of 18 months with minimum side effects. Preliminary evidence suggests that the agent is without effects on the liver or the hypothalamic-pituitary axis. ICI 182780 appears to be a promising new agent for treatment of advanced and early breast cancer.