## **Core Concept**
The question tests knowledge of tumor markers, specifically those 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 various cancers.

## **Why the Correct Answer is Right**
The correct answer, **CA-125**, is a mucin-type glycoprotein present on the surface of many ovarian cancer cells. It is widely used as a tumor marker for ovarian cancer, particularly for monitoring response to treatment and for detecting recurrence. The **CA-125** level is elevated in about 80% of patients with epithelial ovarian cancer, making it a valuable marker for this disease.

## **Why Each Wrong Option is Incorrect**
- **Option A: Carcinoembryonic antigen (CEA)**: While CEA is a tumor marker, it is more commonly associated with colorectal, breast, lung, and other cancers, not specifically ovarian cancer.
- **Option B: Alpha-fetoprotein (AFP)**: AFP is primarily used as a marker for hepatocellular carcinoma and certain germ cell tumors, not ovarian cancer.
- **Option D: Human chorionic gonadotropin (hCG)**: hCG is a marker for choriocarcinoma and certain germ cell tumors but is not specific for ovarian cancer.

## **Clinical Pearl / High-Yield Fact**
A significant clinical pearl is that while **CA-125** is a useful 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 with caution and in the context of clinical findings and imaging studies.

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