Tumor Markers Definition

In this problem, we're asked to identify the best explanation of what tumor markers are for a patient recently diagnosed with cancer. Let's evaluate the four options provided.

Let's look at the first option. It states that markers are enzymes released to prevent cancer. This is incorrect. While some tumor markers are enzymes, they are produced by the tumor itself or by the body in response to cancer; they do not exist to prevent it.

The second option says markers are antigens expressed on the surface of tumor cells. This is a very accurate medical definition. Tumor markers are biological substances, often proteins or antigens, found in blood, urine, or tissues that are produced by cancer cells.

Moving to the third option: it claims markers are doses of vitamins used to fight cancer. This is factually wrong. Tumor markers are diagnostic or monitoring tools, not therapeutic treatments like vitamins.