A tumor marker is anything present in or produced by cancer cells or other cells of the body in response to cancer or certain benign (noncancerous) conditions that provides information about a cancer, such as how aggressive it is, what kind of treatment it may respond to, or whether it is responding to treatment1. Tumor markers have traditionally been proteins or other substances that are made by both normal cells and cancer cells in response to cancer growth or certain benign (noncancerous) conditions1.
