## **Core Concept**
The question tests knowledge of tumor markers associated with ovarian cancer. Tumor markers are substances produced by cancer cells or in response to cancer. They can be used for diagnosing, monitoring, and predicting the outcome of cancer. **CA-125** is a well-established tumor marker for ovarian cancer.

## **Why the Correct Answer is Right**
The correct answer, **CA-125**, is a glycoprotein present on the surface of many ovarian cancer cells. It is widely used as a tumor marker for ovarian cancer, particularly for monitoring disease recurrence and response to treatment. The **CA-125** level is often elevated in patients with ovarian cancer, making it a useful marker for diagnosing and managing the disease.

## **Why Each Wrong Option is Incorrect**
- **Option A:** *Alpha-fetoprotein (AFP)* is a tumor marker primarily associated with hepatocellular carcinoma and certain germ cell tumors, not ovarian cancer.
- **Option B:** *Carcinoembryonic antigen (CEA)* is a tumor marker used for colorectal cancer and other carcinomas but is not specific for ovarian cancer.
- **Option D:** *Prostate-specific antigen (PSA)* is a tumor marker for prostate cancer and has no association with ovarian cancer.

## **Clinical Pearl / High-Yield Fact**
A significant clinical pearl is that while **CA-125** is a valuable marker for ovarian cancer, it is not specific to this disease. Levels can be elevated in various benign conditions, such as endometriosis, during menstruation, and in other cancers. Therefore, it should be interpreted in the context of clinical presentation and imaging findings.

## **Correct Answer:** . **CA-125**