**Core Concept**
Tumor markers are substances produced by cancer cells or in response to cancer that can be detected in the blood or other bodily fluids. They are used to aid in the diagnosis, monitoring, and management of various types of cancer.

**Why the Correct Answer is Right**
Tumor markers can be proteins, enzymes, hormones, or other substances that are produced by cancer cells or in response to cancer. They can be used to detect the presence of cancer, monitor the effectiveness of treatment, and detect recurrence. Examples of tumor markers include CEA (carcinoembryonic antigen), CA-125, and PSA (prostate-specific antigen).

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is not a recognized tumor marker.
**Option B:** This option is incorrect because it is not a tumor marker, but rather a substance produced by the body in response to injury or inflammation.
**Option C:** This option is incorrect because it is a tumor marker used to monitor certain types of cancer, such as colorectal cancer.

**Clinical Pearl / High-Yield Fact**
It's essential to note that tumor markers are not diagnostic, but rather adjunctive tools that can aid in the diagnosis and management of cancer. A positive tumor marker result does not necessarily confirm cancer, and a negative result does not rule out cancer.

**Correct Answer:** D.