tumor marker

(TOO-mer MAR-ker)
A substance found in tissue, blood, bone marrow, or other body fluids that may be a sign of cancer or certain benign (noncancer) conditions. Many tumor markers are proteins made by both normal cells and cancer cells, but they are made in higher amounts by cancer cells. Genetic changes in tumor tissue, such as gene mutations, patterns of gene expression, and other changes in tumor DNA or RNA, are also being used as tumor markers. A tumor marker may be used with other tests to help diagnose cancer. It may also be used to help plan treatment, give a likely prognosis, and find out how well treatment is working or if cancer has come back. Examples of tumor markers include CA-125 (in ovarian cancer), estrogen receptor and progesterone receptor (in breast cancer), CEA (in colon cancer), PCA3 mRNA and PSA (in prostate cancer), and EGFR gene mutation (in non-small cell lung cancer).