**Core Concept**
Tumor markers are substances produced by cancer cells or in response to cancer that can be detected in higher-than-normal amounts in the blood, urine, or tissues of patients with certain types of cancer. These markers can be used for early detection, diagnosis, and monitoring of treatment response.

**Why the Correct Answer is Right**
Tumor markers are specific proteins, enzymes, or hormones that are associated with particular types of cancer. They can be used as diagnostic tools, but their presence or absence does not necessarily confirm or rule out cancer. The correct answer is a substance that is not typically associated with tumor production or cancer detection.

**Why Each Wrong Option is Incorrect**
* **Option A:** Alpha-fetoprotein (AFP) is a tumor marker associated with hepatocellular carcinoma and germ cell tumors.
* **Option B:** Carcinoembryonic antigen (CEA) is a tumor marker used for monitoring colorectal cancer.
* **Option C:** Prostate-specific antigen (PSA) is a tumor marker associated with prostate cancer.

**Clinical Pearl / High-Yield Fact**
Common tumor markers include AFP, CEA, PSA, human chorionic gonadotropin (hCG), and cancer antigen 125 (CA-125), among others. These markers are not specific to cancer and can be elevated in non-cancerous conditions, making them useful but not definitive diagnostic tools.

**Correct Answer:** D.