## **Core Concept**
The question tests knowledge of specific tumor markers associated with various cancers, particularly focusing on prostate cancer. Tumor markers are substances that can be found in higher-than-normal amounts in the blood, urine, or tissues of some patients with certain types of cancer. For prostate cancer, a specific marker is used for diagnosis and monitoring.

## **Why the Correct Answer is Right**
The correct answer, **Prostate-Specific Antigen (PSA)**, is a protein produced by the prostate gland. Elevated levels of PSA in the blood can indicate prostate cancer, though high PSA levels can also result from non-cancerous conditions. PSA is a specific marker for prostate tissue; hence, it serves as a useful marker for prostate cancer.

## **Why Each Wrong Option is Incorrect**
- **Option A:** *Alpha-fetoprotein (AFP)* is primarily associated with hepatocellular carcinoma and certain germ cell tumors, not prostate cancer.
- **Option B:** *Human chorionic gonadotropin (hCG)* is a marker often elevated in choriocarcinoma and some germ cell tumors, not specifically prostate cancer.
- **Option D:** *Carcinoembryonic antigen (CEA)* is a nonspecific marker that can be elevated in a variety of cancers, including colorectal, breast, lung, and others, but is not specific for prostate cancer.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that while PSA is a specific marker for prostate tissue and is used for screening and monitoring prostate cancer, an elevated PSA level does not definitively diagnose cancer. Further diagnostic tests, such as biopsy, are required for a definitive diagnosis. Additionally, PSA levels can be elevated in benign conditions like benign prostatic hyperplasia (BPH) and prostatitis.

## **Correct Answer:** . **Prostate-Specific Antigen (PSA)**