Mechanism of action of tamoxifen is:
**Core Concept**
Tamoxifen is a selective estrogen receptor modulator (SERM) used in the treatment and prevention of breast cancer. It acts by binding to estrogen receptors on cancer cells, thereby inhibiting the growth-promoting effects of estrogen.
**Why the Correct Answer is Right**
Tamoxifen works by competitively binding to estrogen receptors (ER) on breast cancer cells. This binding blocks the action of estrogen, which would otherwise stimulate the growth and proliferation of these cells. The ER-tamoxifen complex then translocates to the nucleus, where it binds to specific DNA sequences, thereby inhibiting the transcription of genes involved in cell growth and proliferation. This mechanism of action is particularly useful in hormone-receptor-positive breast cancer.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because tamoxifen does not work by inhibiting the enzyme aromatase, which is involved in the biosynthesis of estrogen.
* **Option B:** This option is incorrect because tamoxifen does not work by stimulating the growth of cancer cells through the estrogen receptor.
* **Option C:** This option is incorrect because tamoxifen does not work by inhibiting the growth of cancer cells through the androgen receptor.
**Clinical Pearl / High-Yield Fact**
Tamoxifen has both agonist and antagonist effects on estrogen receptors in different tissues, which is why it is often referred to as a "tissue-specific" SERM.
**Correct Answer:** C.