**Core Concept**
RU 486, also known as mifepristone, is a potent antiprogestin medication that blocks the action of progesterone, a hormone essential for maintaining pregnancy. This pharmacological action makes it useful in various clinical applications, particularly in the management of early pregnancy termination.

**Why the Correct Answer is Right**
Mifepristone's mechanism of action involves binding to the progesterone receptor, thereby preventing progesterone from exerting its effects on the uterus. This leads to a decrease in uterine contractions, making it an effective medication for inducing abortion. As a potent antiprogestin, mifepristone is used in combination with prostaglandin analogs to terminate early pregnancy. Additionally, mifepristone has been explored for its potential in the treatment of Cushing's syndrome, a condition characterized by excess cortisol production, due to its ability to block the action of corticosteroids at the glucocorticoid receptor.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is likely incorrect as mifepristone is indeed used in the management of Cushing's syndrome, albeit off-label.

**Option B:** This option may be incorrect as mifepristone has been investigated for its potential use in the treatment of uterine fibroids, although it is not a standard treatment for this condition.

**Option C:** This option is likely incorrect as mifepristone is used in the treatment of uterine fibroids, particularly for managing symptoms associated with this condition.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that mifepristone is not used in the management of ectopic pregnancy, as it does not address the underlying issue of a non-viable pregnancy outside the uterus. Instead, surgical intervention is typically required to manage ectopic pregnancy.

**Correct Answer: A.**