**Question:** A 65 year old male was diagnosed with prostate cancer three years back and was treated by surgery and hormone therapy. Presently he has developed urinary symptoms and progressive backache. What is the tumor marker, which can be indicative of disease relapse -

A. Prostate Specific Antigen (PSA)
B. Carcinoembryonic antigen (CEA)
C. Cancer antigen 125 (CA-125)
D. Alpha-fetoprotein (AFP)

**Correct Answer:** D. Alpha-fetoprotein (AFP)

**Core Concept:** Tumor markers are substances that are produced by cancer cells or in response to cancer, and can be measured in body fluids like blood, urine, or tissue. They can help diagnose, monitor, or predict cancer progression. In the context of prostate cancer, we are interested in PSA (Prostate Specific Antigen), which is produced by prostate cells, and not AFP (Alpha-fetoprotein), which is produced by cells in the liver and placenta, unrelated to prostate cancer.

**Why the Correct Answer is Right:** Alpha-fetoprotein is primarily associated with liver cancers and not prostate cancers. In prostate cancer patients, the primary tumor marker to monitor disease progression is PSA (Prostate Specific Antigen). AFP is not a reliable marker for prostate cancer surveillance.

**Why Each Wrong Option is Incorrect:**

A. PSA (Prostate Specific Antigen) is the most commonly used tumor marker for prostate cancer monitoring, but it is not the correct answer in this case as it is produced by prostate cells.
B. CEA (Carcinoembryonic antigen) is used for monitoring colorectal cancer, not prostate cancer.
C. CA-125 (Cancer antigen 125) is used for ovarian cancer monitoring, not prostate cancer.

**Clinical Pearl:** In prostate cancer patients, monitoring PSA levels is crucial in assessing treatment response and detecting disease recurrence. AFP should not be used in this context, as it is not specific for prostate cancer. Use of inappropriate tumor markers can lead to misinterpretation of disease progression or response to treatment. Always verify the relevance of the marker to the specific cancer type being monitored.