**Question:** Specific Tumor marker is seen in -

A. Carcinoembryonic Antigen (CEA)
B. Prostate Specific Antigen (PSA)
C. Thyroglobulin
D. Catecholamines

**Core Concept:** Tumor markers are substances produced by, or associated with, certain types of cancer cells or benign tumors. They can be detected in blood, urine, or other body fluids, and their elevated levels may indicate the presence of cancer or monitor treatment response.

**Why the Correct Answer is Right:**

Correct Answer: C. Thyroglobulin

Thyroglobulin (Tg) is a glycoprotein produced by thyroid follicular cells. It is a specific tumor marker for thyroid cancer, particularly for differentiated thyroid carcinomas (DTC), including papillary and follicular thyroid cancers. Elevated Tg levels can be detected in the blood of patients after radioactive iodine therapy, indicating the presence of residual or recurrent thyroid cancer.

**Why Each Wrong Option is Incorrect:**

A. Carcinoembryonic Antigen (CEA) - CEA is an oncoprotein that is elevated in colorectal, pancreatic, and breast cancers. Its sensitivity and specificity are lower compared to thyroglobulin for thyroid cancer detection.

B. Prostate Specific Antigen (PSA) - PSA is a prostate-derived glycoprotein and is specific for prostate cancer. It is not a thyroid marker and is not elevated in thyroid cancer.

D. Catecholamines - Catecholamines are neurotransmitters produced by the adrenal glands, not specific for thyroid cancer, and are not tumor markers. They are primarily associated with stress responses and are not useful in diagnosing or monitoring thyroid cancer.

**Clinical Pearl:**

Understanding tumor markers like thyroglobulin is essential for diagnosing and managing thyroid cancer patients. Monitoring thyroglobulin levels can help determine disease status and response to therapy, which is crucial for personalized treatment decisions and prognosis.