**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 breast cancer cells, thereby inhibiting the growth-promoting effects of estrogen.

**Why the Correct Answer is Right**
Tamoxifen is known to cause endometrial cancer, deep vein thrombosis (DVT), and hot flashes as common adverse effects. The mechanism behind these side effects involves tamoxifen's agonist activity on estrogen receptors in the uterus, leading to unopposed estrogen stimulation and increased risk of endometrial cancer. Additionally, tamoxifen's effects on the vascular endothelium contribute to an increased risk of DVT.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because endometrial cancer is a known risk associated with tamoxifen use. The exact reason is tamoxifen's agonist activity on estrogen receptors in the uterus.
**Option B:** This option is incorrect because hot flashes are a common side effect of tamoxifen, likely due to its estrogen receptor modulating effects on thermoregulation centers in the brain.
**Option C:** This option is incorrect because pulmonary embolism (PE) is not a well-documented side effect of tamoxifen, unlike DVT. The increased risk of DVT is a major concern with tamoxifen use.

**Clinical Pearl / High-Yield Fact**
Tamoxifen's risk of endometrial cancer is dose-dependent and can be mitigated by regular gynecological follow-up and consideration of alternative therapies in high-risk patients.

**Correct Answer: C. Pulmonary embolism**