<b>RU486 [mifeprostine] </b>

Anti-progestogens block the action of progesterone at the cellular level through binding to the progesterone receptor.  Mifepristone [RU486] remains the leading compound of this class and is the only one presently used in clinical practice.  Beyond the main action of antiprogestins on human pregnancy, these compounds are useful in the treatment of uterine leiomyomas and endometriosis, and might be useful for contraception. 

Oncologically, tumors like leiomyoarcomas expressing progesterone receptors might be successfully treated with these antihormones. The initial results in the treatment of both benign (fibroids, endometriosis) and malignant (endometrial and ductus carcinoma) gynaecological conditions are encouraging. Clinically achievable doses of RU 486 inhibit endometrial cancer cell lines. Administration of RU486 results in ovarian inhibition and prevention of menstrual cycles. This ovarian inhibition was achieved without estrogen deprivation, and may provide a useful longterm approach to the treatment of steroid-dependent disease processes. Whether this will allow control of LMS growth and progression is unknown. 

Both RU486 [25 mg daily] and leuprolide acetate [lupron depot, 3.75 monthly] are effective in decreasing blood flow to the uterus (increasing resistive index) and decreasing uterine volume due to fibroids after 3 months. A significant decrease in uterine artery blood flow may provide a mechanism for the decrease in uterine size and the decrease in uterine blood loss at the time of surgery for uterine fibroids. Whether RU486 will prove helpful in downgrading LMS tumors is unknown. 

Effective Use of Mifeprostine for control of any aspect of LMS is unproven at this time. There were two members of the LMS list who took it, but there was no slowing of their tumor growth while on it.

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written August 2001
