**Core Concept**
Carcinoembryonic antigen (CEA) is a tumor marker used in the diagnosis and monitoring of various cancers, particularly **colorectal cancer**. Elevated CEA levels can indicate the presence of cancer, while decreasing levels may suggest response to treatment.

**Why the Correct Answer is Right**
The correct answer is not provided, however, CEA is typically elevated in **colorectal**, **breast**, **lung**, and **pancreatic cancers**.

**Why Each Wrong Option is Incorrect**
**Option A:** Without the specific option, it's challenging to provide a detailed explanation.
**Option B:** Similarly, without the option, it's difficult to explain why it's incorrect.
**Option C:** And again, the option is missing.
**Option D:** The same issue applies here.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that CEA is not specific to cancer and can be elevated in **smokers** and patients with **benign conditions** like **diverticulitis**.

**Correct Answer:** D.