## Core Concept
The question targets the pharmacological management of estrogen-dependent breast cancer, focusing on drugs that interfere with estrogen's role in promoting cancer cell growth. Estrogen receptor-positive (ER+) breast cancers are treated with therapies that either reduce estrogen levels or block estrogen receptors.

## Why the Correct Answer is Right
Tamoxifen is a selective estrogen receptor modulator (SERM) that acts as an estrogen receptor antagonist in breast tissue. It is used in the treatment and prevention of estrogen receptor-positive breast cancer. By blocking estrogen receptors on breast cancer cells, tamoxifen inhibits the proliferative effects of estrogen, thereby reducing tumor growth.

## Why Each Wrong Option is Incorrect
* **Option A:** Aromatase inhibitors (e.g., anastrozole, letrozole) are used in the treatment of estrogen-dependent breast cancer but work by a different mechanism. They inhibit the aromatase enzyme, which is crucial for estrogen production in postmenopausal women, thereby reducing estrogen levels.
* **Option B:** This option might represent another class of drugs, but without specifics, it's hard to directly refute. However, if considering other SERMs or hormonal therapies, their primary use or mechanism might not align with tamoxifen's direct anti-estrogenic effects on breast tissue.
* **Option D:** Without specifics, it's challenging to directly address. However, drugs like fulvestrant, which is an estrogen receptor antagonist that works by degrading the estrogen receptor, offer an alternative approach to managing ER+ breast cancer but through a different mechanism than tamoxifen.

## Clinical Pearl / High-Yield Fact
A key point to remember is that tamoxifen is associated with an increased risk of endometrial cancer and venous thromboembolic events. It's also crucial to note that while tamoxifen acts as an antagonist in breast tissue, it has agonist effects in other tissues, such as bone, where it helps maintain bone density.

## Correct Answer: C. Tamoxifen