**Core Concept**
CEA (Carcinoembryonic Antigen) is a tumor marker associated with various types of cancers, particularly colorectal cancer. Elevated levels of CEA can indicate the presence of cancer or monitor its progression.

**Why the Correct Answer is Right**
CEA is a glycoprotein expressed on the surface of certain cancer cells, including colorectal, lung, breast, and ovarian cancer cells. Elevated CEA levels can be seen in patients with these cancers. However, CEA is not specifically elevated in pancreatic cancer, which is the correct answer. This is because pancreatic cancer often expresses different tumor markers, such as CA 19-9.

**Why Each Wrong Option is Incorrect**
**Option A:** Colorectal cancer is associated with elevated CEA levels, making this option incorrect.
**Option B:** Lung cancer can also cause elevated CEA levels, so this option is incorrect.
**Option C:** Breast cancer can express CEA, leading to elevated levels, making this option incorrect.

**Clinical Pearl / High-Yield Fact**
It's essential to note that CEA levels can be elevated in patients with benign conditions, such as inflammatory bowel disease or liver disease, making it a non-specific tumor marker.

**Correct Answer: D. Pancreatic cancer.**