**Core Concept**
Tamoxifen is a selective estrogen receptor modulator (SERM) used in the treatment and prevention of breast cancer. It acts by competing with estrogen for binding to estrogen receptors in breast tissue, thereby inhibiting the growth-promoting effects of estrogen on breast cancer cells.

**Why the Correct Answer is Right**
The correct answer is one of the adverse effects that can occur when using tamoxifen for breast cancer. Tamoxifen can cause endometrial cancer due to its estrogenic effects on the uterus. This is because tamoxifen can stimulate the growth of the endometrium, leading to an increased risk of endometrial cancer. Additionally, tamoxifen can cause venous thromboembolism, hot flashes, and vaginal discharge. The exact mechanism of these effects is not fully understood, but it is thought to be related to tamoxifen's ability to act as an estrogen agonist in certain tissues.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is a known adverse effect of tamoxifen.
**Option B:** This option is incorrect because it is also a known adverse effect of tamoxifen.
**Option C:** This option is incorrect because it is a known adverse effect of tamoxifen.

**Clinical Pearl / High-Yield Fact**
It's essential to note that the risk of endometrial cancer associated with tamoxifen is increased in postmenopausal women, especially those with a history of estrogen receptor-positive breast cancer.

**Correct Answer:** D