Definition

A substance, such as a protein or fragment of DNA, that is released into a person’s blood, urine, other body fluid, or stool by tumor cells or other cells of the body. Circulating tumor markers may be a sign of cancer or certain benign (noncancer) conditions. Measurements of circulating tumor marker levels in blood or other body fluid may be used along with results of other tests, such as biopsies and imaging, to help diagnose some types of cancer. Knowing the levels of circulating tumor markers may also help plan cancer treatment, make a likely prognosis, and find out how well treatment is working or if cancer has come back. Examples of circulating tumor markers include CA-125 (in ovarian cancer), calcitonin (in medullary thyroid cancer), EGFR mutations (in lung cancer), and beta-2-microglobulin (in multiple myeloma, chronic lymphocytic leukemia, and some lymphomas).