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Effects of Idoxifene

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John Han-Chih Chang, MD and Kenneth Blank, MD
Last Modified: November 1, 2001

Dear OncoLink "Ask the Experts,"
Recently my sister who has breast cancer at an advanced stage, was invited to participate in a clinical trial:

Title : A multicenter, ramdomized, double blind study of idoxifene 40mg/day versus tamoxifen 20mg/day as first line hormonal therapy in postmenopausal women with metastatic breast cancer.

I have tried to search for more information regarding idoxifene from the internet but not much information is available. I will be most obliged if you can provide me with more information about idoxifene and results of research that have been carried out based on this drug. I understand that idoxifene is a new drug for cancer treatment. What about side effects ? Recently studies have shown that tamoxifen increases the probability of uterine cancer. How about idoxifene?  
Thank you very much.

John Han-Chih Chang, MD and Kenneth Blank, MD OncoLink's Editorial Assistants, respond:

Thank you for your interest and question.  
Idoxifene is a very novel anti-breast cancer agent. Most of the published data come from cellular in vitro and animal studies. There was one published pilot study from the London, England on the significant yet limited success of the drug on patients with metastatic breast cancer who have been treated with tamoxifen.

Idoxifene is given at a dosage of 20 mg/day (range 10 - 60mg). The initial half-life is 15hrs and terminal half-life is 23.3 days. The side effects of idoxifene appear to be similar to tamoxifen. The potential benefit of idoxifene over tamoxifen is in the rate of secondary endometial cancer and liver tumors. In cellular and animal studies, idoxifene appear to be less carcinogenic and tumoregenic with the same anti-luteninizing hormone and anti-follicle-stimulating hormone effect.

As with any new therapy, it must be tested in a randomized fashion in order to fully answer the question of whether it is a legitimate treatment. Another source of information on idoxifene would be available through your chemotherapy doctor. He or she should have a patient information sheet that details the study and the side effects and the possible benefits.

Please refer to OncoLink's section on tamoxifen and its relation to endometrial cancer.