**Core Concept**
Aromatase inhibitors (AIs) are a class of medications used in the treatment of hormone receptor-positive breast cancer, particularly in postmenopausal women. They work by inhibiting the enzyme aromatase, which is responsible for converting androgens into estrogens, thus reducing estrogen levels in the body and slowing down the growth of breast cancer cells.

**Why the Correct Answer is Right**
Aromatase inhibitors, such as anastrozole, letrozole, and exemestane, bind to the aromatase enzyme and irreversibly inhibit its activity. This leads to a decrease in the production of estrogens, including estradiol, which is a potent stimulator of breast cancer cell growth. By reducing estrogen levels, aromatase inhibitors can help slow down the growth of hormone receptor-positive breast cancer cells and prevent the progression of the disease. This mechanism of action makes aromatase inhibitors a valuable treatment option for postmenopausal women with hormone receptor-positive breast cancer.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify the mechanism of action of aromatase inhibitors. While it may be a true statement, it does not address the underlying principle of how AIs work.

**Option B:** This option is incorrect because it is a partial truth. While aromatase inhibitors do reduce estrogen levels, they do not directly inhibit estrogen receptors. Estrogen receptors are targets for other types of breast cancer therapies, such as selective estrogen receptor modulators (SERMs).

**Option C:** This option is incorrect because it is a side effect of aromatase inhibitors, not their primary mechanism of action. Hot flashes, joint pain, and osteoporosis are common side effects of AIs, but they do not explain how these medications work.

**Clinical Pearl / High-Yield Fact**
Aromatase inhibitors are most effective in postmenopausal women with hormone receptor-positive breast cancer, as they can significantly reduce estrogen levels and slow down tumor growth. In premenopausal women, AIs may be used in combination with ovarian suppression to reduce estrogen levels.

**Correct Answer:** C.